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\input texinfo @c *texinfo*


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@c %**start of header


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@setfilename bc.info


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@settitle bc Command Manual


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@c %**end of header


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@include texiver.incl


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@c This file has the new style title page commands.


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@c Run `makeinfo' rather than `texinfoformatbuffer'.


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@smallbook


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@c tex


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@c \overfullrule=0pt


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@c end tex


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@ifinfo


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@direntry


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* bc: (bc). An arbitrary precision calculator language.


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@end direntry


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@end ifinfo


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@titlepage


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@title @command{bc}


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@subtitle an arbitrary precision calculator language


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@subtitle version @value{BC_VERSION}


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@author Philip A. Nelson


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@page


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This manual documents @command{bc}, an arbitrary precision calculator language.


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This manual is part of GNU @command{bc}.@*


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@sp 4


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Copyright (C) 1991, 1992, 1993, 1994, 1997, 2003, 2006 Free Software Foundation, Inc.


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51 Franklin Street, Fifth Floor, Boston, MA 021101301 USA.


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Permission is granted to make and distribute verbatim copies of


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this manual provided the copyright notice and this permission notice


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are preserved on all copies.


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@ignore


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Permission is granted to process this file through TeX and print the


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results, provided the printed document carries copying permission


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notice identical to this one except for the removal of this paragraph


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(this paragraph not being relevant to the printed manual).


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@end ignore


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Permission is granted to copy and distribute modified versions of this


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manual under the conditions for verbatim copying, provided that the entire


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resulting derived work is distributed under the terms of a permission


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notice identical to this one.


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Permission is granted to copy and distribute translations of this manual


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into another language, under the above conditions for modified versions,


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except that this permission notice may be stated in a translation approved


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by the Foundation.


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You may contact the author by:


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email: @email{phil@@cs.wwu.edu}@*


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usmail: Philip A. Nelson@*


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Computer Science Department, 9062@*


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Western Washington University@*


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Bellingham, WA 982269062


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@end titlepage


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@node Top, Introduction, (dir), (dir)


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@menu


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* Introduction::


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* Basic Elements::


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* Expressions::


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* Statements::


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* Functions::


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* Examples::


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* Readline and Libedit Options::


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* Comparison with Other Implementations::


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* Limits::


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* Environment Variables::


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@end menu


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@node Introduction, Basic Elements, Top, Top


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@chapter Introduction


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@menu


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* Description::


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* Command Line Options::


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@end menu


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@node Description, Command Line Options, Introduction, Introduction


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@section Description


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@command{bc} [ hlwsqv ] [longoptions] [ @var{ file ...} ]


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@command{bc} is a language that supports arbitrary precision numbers


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with interactive execution of statements. There are some similarities


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in the syntax to the C programming language.


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A standard math library is available by command line option.


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If requested, the math library is defined before processing any files.


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@command{bc} starts by processing code from all the files listed


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on the command line in the order listed. After all files have been


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processed, @command{bc} reads from the standard input. All code is


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executed as it is read. (If a file contains a command to halt the


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processor, @command{bc} will never read from the standard input.)


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This version of @command{bc} contains several extensions beyond


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traditional @command{bc} implementations and the POSIX draft standard.


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Command line options can cause these extensions to print a warning or to


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be rejected. This document describes the language accepted by this


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processor. Extensions will be identified as such.


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The author would like to thank Steve Sommars


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(@email{Steve.Sommars@@att.com}) for his extensive help in testing the


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implementation. Many great suggestions were given. This is a much


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better product due to his involvement.


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Email bug reports to @email{bugbc@@gnu.org}. Be sure to include


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the word ``bc'' somewhere in the ``Subject:'' field.


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@node Command Line Options, Numbers, Description, Introduction


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@section Command Line Options


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@command{bc} takes the following options from the command line:


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@table @code


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@item h, help


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Print the usage and exit.


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@item l, mathlib


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Define the standard math library.


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@item w, warn


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Give warnings for extensions to POSIX @command{bc}.


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@item s, standard


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Process exactly the POSIX @command{bc} language.


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@item q, quiet


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Do not print the normal GNU @command{bc} welcome.


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@item v, version


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Print the version number and copyright and quit.


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@end table


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@node Basic Elements, Expressions, Introduction, Top


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@chapter Basic Elements


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@menu


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* Numbers::


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* Variables::


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* Comments::


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@end menu


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@node Numbers, Variables, Command Line Options, Basic Elements


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@section Numbers


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The most basic element in @command{bc} is the number. Numbers are


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arbitrary precision numbers. This precision is both in the integer


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part and the fractional part. All numbers are represented internally


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in decimal and all computation is done in decimal. (This version


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truncates results from divide and multiply operations.) There are two


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attributes of numbers, the length and the scale. The length is the


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total number of digits used by @command{bc} to represent a number and


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the scale is the total number of decimal digits after the decimal


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point. For example, .000001 has a length of 6 and scale of 6, while


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1935.000 has a length of 7 and a scale of 3.


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@node Variables, Comments, Numbers, Basic Elements


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@section Variables


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Numbers are stored in two types of variables, simple variables and


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arrays. Both simple variables and array variables are named. Names


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begin with a letter followed by any number of letters, digits and


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underscores. All letters must be lower case. (Full alphanumeric


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names are an extension. In POSIX @command{bc} all names are a single


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lower case letter.) The type of variable is clear by the context


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because all array variable names will be followed by brackets ( [ ] ).


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There are four special variables, @var{scale}, @var{ibase}, @var{obase}, and


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@var{last}. @var{scale} defines how some operations use digits after the


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decimal point. The default value of @var{scale} is 0. @var{ibase}


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and @var{obase} define the conversion base for input and output


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numbers. The default for both input and output is base 10.


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@var{last} (an extension) is a variable that has the value of the last


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printed number. These will be discussed in further detail where


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appropriate. All of these variables may have values assigned to them


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as well as used in expressions.


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@node Comments, , Variables, Basic Elements


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@section Comments


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Comments in @command{bc} start with the characters @code{/*} and end with


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the characters @code{*/}. Comments may start anywhere and appear as a


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single space in the input. (This causes comments to delimit other


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input items. For example, a comment can not be found in the middle of


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a variable name.) Comments include any newlines (end of line) between


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the start and the end of the comment.


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To support the use of scripts for @command{bc}, a single line comment has been


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added as an extension. A single line comment starts at a @code{#}


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character and continues to the next end of the line. The end of line


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character is not part of the comment and is processed normally.


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@node Expressions, Statements, Basic Elements, Top


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@chapter Expressions


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@menu


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* About Expressions and Special Variables::


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* Basic Expressions::


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* Relational Expressions::


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* Boolean Expressions::


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* Precedence::


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* Special Expressions::


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@end menu


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@node About Expressions and Special Variables, Basic Expressions, Expressions, Expressions


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@section About Expressions and Special Variables


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The numbers are manipulated by expressions and statements. Since


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the language was designed to be interactive, statements and expressions


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are executed as soon as possible. There is no main program. Instead,


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code is executed as it is encountered. (Functions, discussed in


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detail later, are defined when encountered.)


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A simple expression is just a constant. @command{bc} converts constants


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into internal decimal numbers using the current input base, specified by


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the variable @var{ibase}. (There is an exception in functions.) The


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legal values of @var{ibase} are 2 through 36. (Bases greater than


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16 are an extension.) Assigning a value outside


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this range to @var{ibase} will result in a value of 2 or 36. Input


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numbers may contain the characters 09 and AZ. (Note: They must be


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capitals. Lower case letters are variable names.) Single digit numbers


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always have the value of the digit regardless of the value of


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@var{ibase}. (i.e. A = 10.) For multidigit numbers, @command{bc}


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changes all input digits greater or equal to @var{ibase} to the value of


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@var{ibase}1. This makes the number @code{ZZZ} always be the largest


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3 digit number of the input base.


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Full expressions are similar to many other high level languages.


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Since there is only one kind of number, there are no rules for mixing


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types. Instead, there are rules on the scale of expressions. Every


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expression has a scale. This is derived from the scale of original


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numbers, the operation performed and in many cases, the value of the


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variable @var{scale}. Legal values of the variable @var{scale} are


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0 to the maximum number representable by a C integer.


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@node Basic Expressions, Relational Expressions, About Expressions and Special Variables, Expressions


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@section Basic Expressions


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In the following descriptions of legal expressions, "expr" refers to a


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complete expression and "@var{var}" refers to a simple or an array variable.


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A simple variable is just a


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@var{name}


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and an array variable is specified as


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@var{name}[@var{expr}]


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Unless specifically mentioned the scale of the result is the maximum


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scale of the expressions involved.


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@table @code


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@item  expr


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The result is the negation of the expression.


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@item ++ @var{var}


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The variable is incremented by one and the new value is the result of


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the expression.


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@item  @var{var}


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The variable


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is decremented by one and the new value is the result of the


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expression.


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@item @var{var} ++


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The result of the expression is the value of


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the variable and then the variable is incremented by one.


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@item @var{var} 


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The result of the expression is the value of the variable and then


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the variable is decremented by one.


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@item expr + expr


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The result of the expression is the sum of the two expressions.


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@item expr  expr


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The result of the expression is the difference of the two expressions.


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@item expr * expr


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The result of the expression is the product of the two expressions.


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@item expr / expr


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The result of the expression is the quotient of the two expressions.


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The scale of the result is the value of the variable @code{scale}


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@item expr % expr


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The result of the expression is the "remainder" and it is computed in the


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following way. To compute a%b, first a/b is computed to @var{scale}


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digits. That result is used to compute a(a/b)*b to the scale of the


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maximum of @var{scale}+scale(b) and scale(a). If @var{scale} is set


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to zero and both expressions are integers this expression is the


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integer remainder function.


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@item expr ^ expr


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The result of the expression is the value of the first raised to the


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second. The second expression must be an integer. (If the second


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expression is not an integer, a warning is generated and the


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expression is truncated to get an integer value.) The scale of the


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result is @var{scale} if the exponent is negative. If the exponent


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is positive the scale of the result is the minimum of the scale of the


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first expression times the value of the exponent and the maximum of


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@var{scale} and the scale of the first expression. (e.g. scale(a^b)


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= min(scale(a)*b, max(@var{scale}, scale(a))).) It should be noted


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that expr^0 will always return the value of 1.


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@item ( expr )


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This alters the standard precedence to force the evaluation of the


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expression.


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@item @var{var} = expr


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The variable is assigned the value of the expression.


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@item @var{var} <op>= expr


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This is equivalent to "@var{var} = @var{var} <op> expr" with the


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exception that the "@var{var}" part is evaluated only once. This can


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make a difference if "@var{var}" is an array.


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@end table


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@node Relational Expressions, Boolean Expressions, Basic Expressions, Expressions


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@section Relational Expressions


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Relational expressions are a special kind of expression that always


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evaluate to 0 or 1, 0 if the relation is false and 1 if the relation is


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true. These may appear in any legal expression. (POSIX @command{bc}


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requires that relational expressions are used only in @code{if},


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@code{while}, and @code{for} statements and that only one relational


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test may be done in them.) The relational operators are


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@table @code


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@item expr1 < expr2


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The result is 1 if expr1 is strictly less than expr2.


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@item expr1 <= expr2


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The result is 1 if expr1 is less than or equal to expr2.


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@item expr1 > expr2


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The result is 1 if expr1 is strictly greater than expr2.


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@item expr1 >= expr2


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The result is 1 if expr1 is greater than or equal to expr2.


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@item expr1 == expr2


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The result is 1 if expr1 is equal to expr2.


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@item expr1 != expr2


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The result is 1 if expr1 is not equal to expr2.


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@end table


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@node Boolean Expressions, Precedence, Relational Expressions, Expressions


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@section Boolean Expressions


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Boolean operations are also legal. (POSIX @command{bc} does NOT have


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boolean operations). The result of all boolean operations are 0 and 1


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(for false and true) as in relational expressions. The boolean


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operators are:


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@table @code


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@item !expr


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The result is 1 if expr is 0.


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@item expr && expr


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The result is 1 if both expressions are nonzero.


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@item expr  expr


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The result is 1 if either expression is nonzero.


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@end table


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@node Precedence, Special Expressions, Boolean Expressions, Expressions


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@section Precedence


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The expression precedence is as follows: (lowest to highest)


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@example


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 operator, left associative


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&& operator, left associative


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! operator, nonassociative


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Relational operators, left associative


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Assignment operator, right associative


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+ and  operators, left associative


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*, / and % operators, left associative


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^ operator, right associative


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unary  operator, nonassociative


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++ and  operators, nonassociative


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@end example


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This precedence was chosen so that POSIX compliant @command{bc} programs


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will run correctly. This will cause the use of the relational and


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logical operators to have some unusual behavior when used with


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assignment expressions. Consider the expression:


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@example


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a = 3 < 5


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@end example


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Most C programmers would assume this would assign the result of "3 <


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5" (the value 1) to the variable "a". What this does in @command{bc} is


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assign the value 3 to the variable "a" and then compare 3 to 5. It is


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best to use parentheses when using relational and logical operators


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with the assignment operators.


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@node Special Expressions, , Precedence, Expressions


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@section Special Expressions


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There are a few more special expressions that are provided in


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@command{bc}. These have to do with userdefined functions and standard


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functions. They all appear as


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"@var{name}@code{(}@var{parameters}@code{)}". @xref{Functions}, for


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userdefined functions. The standard functions are:


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@table @code


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@item length ( @var{expression} )


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The value of the length function is the number of significant digits in the


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expression.


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@item read ( )


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The @code{read} function (an extension) will read a number from the


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standard input, regardless of where the function occurs. Beware, this


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can cause problems with the mixing of data and program in the standard


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input. The best use for this function is in a previously written


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program that needs input from the user, but never allows program code to


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be input from the user. The value of the @code{read} function is the


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number read from the standard input using the current value of the


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variable @var{ibase} for the conversion base.


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@item scale ( @var{expression} )


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The value of the @code{scale} function is the number of digits after the


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decimal point in the expression.


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@item sqrt ( @var{expression} )


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The value of the @code{sqrt} function is the square root of the


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expression. If the expression is negative, a run time error is


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generated.


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@end table


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@node Statements, Functions, Expressions, Top


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@chapter Statements


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@menu


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* Pseudo Statements::


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@end menu


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Statements (as in most algebraic languages) provide the sequencing of


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expression evaluation. In @command{bc} statements are executed "as soon


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as possible." Execution happens when a newline in encountered and there


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is one or more complete statements. Due to this immediate execution,


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newlines are very important in @command{bc}. In fact, both a semicolon


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and a newline are used as statement separators. An improperly placed


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newline will cause a syntax error. Because newlines are statement


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separators, it is possible to hide a newline by using the backslash


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character. The sequence "\<nl>", where <nl> is the newline appears to


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@command{bc} as whitespace instead of a newline. A statement list is a


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series of statements separated by semicolons and newlines. The


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following is a list of @command{bc} statements and what they do: (Things


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enclosed in brackets ( [ ] ) are optional parts of the statement.)


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@table @code


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@item @var{expression}


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This statement does one of two things. If the expression starts with


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"<variable> <assignment> ...", it is considered to be an assignment


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statement. If the expression is not an assignment statement, the


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expression is evaluated and printed to the output. After the number is


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printed, a newline is printed. For example, "a=1" is an assignment


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statement and "(a=1)" is an expression that has an embedded assignment.


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All numbers that are printed are printed in the base specified by the


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variable @var{obase}. The legal values for @var{obase} are 2 through


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BC_BASE_MAX (@pxref{Environment Variables}). For bases 2 through 16,


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the usual method of writing numbers is used. For bases greater than 16,


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@command{bc} uses a multicharacter digit method of printing the numbers


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where each higher base digit is printed as a base 10 number. The


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multicharacter digits are separated by spaces. Each digit contains the


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number of characters required to represent the base ten value of


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"@var{obase} 1". Since numbers are of arbitrary precision, some


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numbers may not be printable on a single output line. These long


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numbers will be split across lines using the "\" as the last character


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on a line. The maximum number of characters printed per line is 70.


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Due to the interactive nature of @command{bc}, printing a number causes


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the side effect of assigning the printed value to the special variable


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@var{last}. This allows the user to recover the last value printed


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without having to retype the expression that printed the number.


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Assigning to @var{last} is legal and will overwrite the last printed


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value with the assigned value. The newly assigned value will remain


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until the next number is printed or another value is assigned to


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@var{last}. (Some installations may allow the use of a single period


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(.) which is not part of a number as a short hand notation for for


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@var{last}.)


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@item @var{string}


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The string is printed to the output. Strings start with a double quote


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character and contain all characters until the next double quote character.


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All characters are taken literally, including any newline. No newline


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character is printed after the string.


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@item print @var{list}


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The @code{print} statement (an extension) provides another method of


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output. The @var{list} is a list of strings and expressions separated by


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commas. Each string or expression is printed in the order of the list.


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No terminating newline is printed. Expressions are evaluated and their


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value is printed and assigned to the variable @code{last}. Strings in


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the print statement are printed to the output and may contain special


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characters. Special characters start with the backslash character (\e).


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The special characters recognized by @command{bc} are "a" (alert or


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bell), "b" (backspace), "f" (form feed), "n" (newline), "r" (carriage


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return), "q" (double quote), "t" (tab), and "\e" (backslash). Any other


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character following the backslash will be ignored.


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@item @{ @var{statement_list} @}


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This is the compound statement. It allows multiple statements to be


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grouped together for execution.


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@item if ( @var{expression} ) @var{statement1} [else @var{statement2}]


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The if statement evaluates the expression and executes statement1 or


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statement2 depending on the value of the expression. If the expression


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is nonzero, statement1 is executed. If statement2 is present and


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the value of the expression is 0, then statement2 is executed. (The


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@code{else} clause is an extension.)


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@item while ( @var{expression} ) @var{statement}


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The while statement will execute the statement while the expression


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is nonzero. It evaluates the expression before each execution of


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the statement. Termination of the loop is caused by a zero


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expression value or the execution of a @code{break} statement.


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@item for ( [@var{expression1}] ; [@var{expression2}] ; [@var{expression3}] ) @var{statement}


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The @code{for} statement controls repeated execution of the statement.


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@var{Expression1} is evaluated before the loop. @var{Expression2} is


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evaluated before each execution of the statement. If it is nonzero,


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the statement is evaluated. If it is zero, the loop is terminated.


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After each execution of the statement, @var{expression3} is evaluated


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before the reevaluation of expression2. If @var{expression1} or


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@var{expression3} are missing, nothing is evaluated at the point they


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would be evaluated. If @var{expression2} is missing, it is the same as


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substituting the value 1 for @var{expression2}. (The optional


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expressions are an extension. POSIX @command{bc} requires all three


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expressions.) The following is equivalent code for the @code{for}


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statement:


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@example


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expression1;


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while (expression2) @{


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statement;


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expression3;


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@}


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@end example


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@item break


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This statement causes a forced exit of the most recent enclosing @code{while}


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statement or @code{for} statement.


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@item continue


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The @code{continue} statement (an extension) causes the most recent enclosing


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@code{for} statement to start the next iteration.


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@item halt


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The @code{halt} statement (an extension) is an executed statement that


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causes the @command{bc} processor to quit only when it is executed. For


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example, "if (0 == 1) halt" will not cause @command{bc} to terminate


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because the @code{halt} is not executed.


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@item return


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Return the value 0 from a function. (@xref{Functions}.)


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@item return ( @var{expression} )


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Return the value of the expression from a function. (@xref{Functions}.)


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As an extension, the parenthesis are not required.


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@end table


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@node Pseudo Statements, , Statements, Statements


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@section Pseudo Statements


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These statements are not statements in the traditional sense. They are


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not executed statements. Their function is performed at "compile" time.


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@table @code


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@item limits


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Print the local limits enforced by the local version of @command{bc}. This


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is an extension.


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70b277 


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@item quit


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When the @code{quit} statement is read, the @command{bc} processor


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is terminated, regardless of where the @code{quit} statement is found. For


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example, "if (0 == 1) quit" will cause @command{bc} to terminate.


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@item warranty


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Print a longer warranty notice. This is an extension.


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@end table


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@node Functions, Examples, Statements, Top


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@chapter Functions


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@menu


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* Math Library Functions::


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@end menu


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70b277 


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Functions provide a method of defining a computation that can be


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executed later. Functions in @command{bc} always compute a value and


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return it to the caller. Function definitions are "dynamic" in the


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sense that a function is undefined until a definition is encountered in


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the input. That definition is then used until another definition


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function for the same name is encountered. The new definition then


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replaces the older definition. A function is defined as follows:


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70b277 


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70b277 
@example


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@code{define} @var{name} @code{(} @var{parameters} @code{)} @code{@{} @var{newline}


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@var{auto_list statement_list} @code{@}}


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@end example


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70b277 


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A function call is just an expression of the form


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"@code{name} @code{(}@var{parameters}@code{)}".


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70b277 


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Parameters are numbers or arrays (an extension). In the function definition,


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zero or more parameters are defined by listing their names separated by


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commas. All parameters are call by value parameters.


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Arrays are specified in the parameter definition by


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the notation "@var{name}@code{[ ]}". In the function call, actual parameters


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are full expressions for number parameters. The same notation is used


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for passing arrays as for defining array parameters. The named array is


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passed by value to the function. Since function definitions are dynamic,


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parameter numbers and types are checked when a function is called. Any


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mismatch in number or types of parameters will cause a runtime error.


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A runtime error will also occur for the call to an undefined function.


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70b277 


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The @var{auto_list} is an optional list of variables that are for


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"local" use. The syntax of the auto list (if present) is "@code{auto}


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@var{name}, ... ;". (The semicolon is optional.) Each @var{name} is


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the name of an auto variable. Arrays may be specified by using the


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same notation as used in parameters. These variables have their


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values pushed onto a stack at the start of the function. The


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variables are then initialized to zero and used throughout the


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execution of the function. At function exit, these variables are


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popped so that the original value (at the time of the function call)


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of these variables are restored. The parameters are really auto


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variables that are initialized to a value provided in the function


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call.


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70b277 
Auto variables are different than traditional local variables


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because if function A calls function B, B may access function


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A's auto variables by just using the same name, unless function B has


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called them auto variables. Due to the fact that auto variables and


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parameters are pushed onto a stack, @command{bc} supports recursive functions.


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70b277 


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The function body is a list of @command{bc} statements. Again, statements


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are separated by semicolons or newlines. Return statements cause the


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termination of a function and the return of a value. There are two


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versions of the return statement. The first form, "@code{return}", returns


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the value 0 to the calling expression. The second form,


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"@code{return} ( @var{expression} )", computes the value of the expression


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and returns that value to the calling expression. There is an implied


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"@code{return} (0)" at the end of every function. This allows a function


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to terminate and return 0 without an explicit @code{return} statement.


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70b277 


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Functions also change the usage of the variable @var{ibase}. All


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constants in the function body will be converted using the value of


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@var{ibase} at the time of the function call. Changes of @var{ibase}


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will be ignored during the execution of the function except for the


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standard function @code{read}, which will always use the current value


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of @var{ibase} for conversion of numbers.


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70b277 


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70b277 
Several extensions have been added to functions. First, the format of


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the definition has been slightly relaxed. The standard requires the


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opening brace be on the same line as the @code{define} keyword and all


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other parts must be on following lines. This version of @command{bc}


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will allow any number of newlines before and after the opening brace of


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the function. For example, the following definitions are legal.


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70b277 


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70b277 
@example


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define d (n) @{ return (2*n); @}


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define d (n)


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@{ return (2*n); @}


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70b277 
@end example


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70b277 


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70b277 
Functions may be defined as @code{void}. A void


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funtion returns no value and thus may not be used in any place that needs


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a value. A void function does not produce any output when called by itself


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on an input line. The key word @code{void} is placed between the key word


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@code{define} and the function name. For example, consider the following


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session.


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70b277 


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70b277 
@example


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define py (y) @{ print ">", y, "<", "\n"; @}


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define void px (x) @{ print ">", x, "<", "\n"; @}


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py(1)


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>1<


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0


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px(1)


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>1<


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70b277 
@end example


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70b277 


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Since @code{py} is not a void function, the call of @code{py(1)} prints


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the desired output and then prints a second line that is the value of


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the function. Since the value of a function that is not given an


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explicit return statement is zero, the zero is printed. For @code{px(1)},


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no zero is printed because the function is a void function.


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70b277 


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70b277 
Also, call by variable for arrays was added. To declare a


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call by variable array, the declaration of the array parameter in the


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function definition looks like "@code{*}@var{name}@code{[]}". The call


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to the function remains the same as call by value arrays.


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70b277 


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@node Math Library Functions, , Functions, Functions


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70b277 
@section Math Library Functions


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70b277 


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If @command{bc} is invoked with the @code{l} option, a math library is


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preloaded and the default @var{scale} is set to 20. The math functions will


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calculate their results to the scale set at the time of their call. The


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math library defines the following functions:


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70b277 


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70b277 
@table @code


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70b277 
@item s (@var{x})


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70b277 
The sine of @var{x}, @var{x} is in radians.


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70b277 


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@item c (@var{x})


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70b277 
The cosine of @var{x}, @var{x} is in radians.


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70b277 


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@item a (@var{x})


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The arctangent of @var{x}, arctangent returns radians.


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70b277 


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70b277 
@item l (@var{x})


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The natural logarithm of @var{x}.


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70b277 


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@item e (@var{x})


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The exponential function of raising @var{e} to the value @var{x}.


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70b277 


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@item j (@var{n}, @var{x})


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70b277 
The Bessel function of integer order @var{n} of @var{x}.


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70b277 
@end table


Packit 
70b277 


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70b277 
@node Examples, Readline and Libedit Options, Functions, Top


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70b277 
@chapter Examples


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70b277 


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70b277 
In /bin/sh, the following will assign the value of "pi" to the shell


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variable @var{pi}.


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70b277 
@example


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70b277 


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70b277 
pi=$(echo "scale=10; 4*a(1)"  bc l)


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70b277 


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70b277 
@end example


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70b277 


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70b277 
The following is the definition of the exponential function used in the


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70b277 
math library. This function is written in POSIX @command{bc}.


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70b277 


Packit 
70b277 
@example


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70b277 


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70b277 
scale = 20


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70b277 


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70b277 
/* Uses the fact that e^x = (e^(x/2))^2


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70b277 
When x is small enough, we use the series:


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70b277 
e^x = 1 + x + x^2/2! + x^3/3! + ...


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70b277 
*/


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70b277 


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70b277 
define e(x) @{


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70b277 
auto a, d, e, f, i, m, v, z


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70b277 


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70b277 
/* Check the sign of x. */


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70b277 
if (x<0) @{


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70b277 
m = 1


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70b277 
x = x


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70b277 
@}


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70b277 


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70b277 
/* Precondition x. */


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70b277 
z = scale;


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70b277 
scale = 4 + z + .44*x;


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70b277 
while (x > 1) @{


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70b277 
f += 1;


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70b277 
x /= 2;


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70b277 
@}


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70b277 


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70b277 
/* Initialize the variables. */


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70b277 
v = 1+x


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70b277 
a = x


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70b277 
d = 1


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70b277 


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70b277 
for (i=2; 1; i++) @{


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70b277 
e = (a *= x) / (d *= i)


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70b277 
if (e == 0) @{


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70b277 
if (f>0) while (f) v = v*v;


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70b277 
scale = z


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70b277 
if (m) return (1/v);


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70b277 
return (v/1);


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70b277 
@}


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70b277 
v += e


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70b277 
@}


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70b277 
@}


Packit 
70b277 


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70b277 
@end example


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70b277 


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70b277 
The following is code that uses the extended features of @command{bc} to


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70b277 
implement a simple program for calculating checkbook balances. This


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70b277 
program is best kept in a file so that it can be used many times


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70b277 
without having to retype it at every use.


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70b277 


Packit 
70b277 
@example


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70b277 


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70b277 
scale=2


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70b277 
print "\nCheck book program\n!"


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70b277 
print " Remember, deposits are negative transactions.\n"


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70b277 
print " Exit by a 0 transaction.\n\n"


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70b277 


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70b277 
print "Initial balance? "; bal = read()


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70b277 
bal /= 1


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70b277 
print "\n"


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70b277 
while (1) @{


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70b277 
"current balance = "; bal


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70b277 
"transaction? "; trans = read()


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70b277 
if (trans == 0) break;


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70b277 
bal = trans


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70b277 
bal /= 1


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70b277 
@}


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70b277 
quit


Packit 
70b277 


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70b277 
@end example


Packit 
70b277 


Packit 
70b277 


Packit 
70b277 
The following is the definition of the recursive factorial function.


Packit 
70b277 


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70b277 
@example


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70b277 


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70b277 
define f (x) @{


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70b277 
if (x <= 1) return (1);


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70b277 
return (f(x1) * x);


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70b277 
@}


Packit 
70b277 


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70b277 
@end example


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70b277 


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70b277 
@node Readline and Libedit Options, Comparison with Other Implementations, Examples, Top


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70b277 
@chapter Readline and Libedit Options


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70b277 


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70b277 
GNU @command{bc} can be compiled (via a configure option) to use the GNU


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@command{readline} input editor library or the BSD @command{libedit}


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library. This allows the user to do


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more editing of lines before sending them to @command{bc}. It also


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allows for a history of previous lines typed. When this option is


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selected, @command{bc} has one more special variable. This special


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variable, @var{history} is the number of lines of history retained. A


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value of 1 means that an unlimited number of history lines are


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retained. This is the default value. Setting the value of


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@var{history} to a positive number restricts the number of history lines


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to the number given. The value of 0 disables the history feature. For


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more information, read the user manuals for the GNU @command{readline},


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@command{history} and BSD @command{libedit} libraries. One can not


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enable both @command{readline} and @command{libedit} at the same time.


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@node Comparison with Other Implementations, Limits, Readline and Libedit Options, Top


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@chapter Comparison with Other Implementations


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This version of @command{bc} was implemented from the POSIX P1003.2/D11


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draft and contains several differences and extensions relative to the


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draft and traditional implementations. It is not implemented in the


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traditional way using @command{dc}. This version is a single process


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which parses and runs a byte code translation of the program. There is


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an "undocumented" option (c) that causes the program to output the byte


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code to the standard output instead of running it. It was mainly used


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for debugging the parser and preparing the math library.


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A major source of differences is extensions, where a feature is extended


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to add more functionality and additions, where new features are added.


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The following is the list of differences and extensions.


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@table @asis


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@item LANG environment


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This version does not conform to the POSIX standard in the processing


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of the LANG environment variable and all environment variables starting


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with LC_.


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@item names


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Traditional and POSIX @command{bc}


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have single letter names for functions, variables and arrays. They have


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been extended to be multicharacter names that start with a letter and


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may contain letters, numbers and the underscore character.


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@item Strings


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Strings are not allowed to contain NUL characters. POSIX says all characters


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must be included in strings.


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@item last


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POSIX @command{bc} does not have a \fBlast variable. Some implementations


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of @command{bc} use the period (.) in a similar way.


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@item comparisons


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POSIX @command{bc} allows comparisons only in the @code{if} statement,


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the @code{while} statement, and the second expression of the @code{for}


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statement. Also, only one relational operation is allowed in each of


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those statements.


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@item @code{if} statement, @code{else} clause


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POSIX @command{bc} does not have an @code{else} clause.


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@item @code{for} statement


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POSIX @command{bc} requires all expressions to be present in the


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@code{for} statement.


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@item @code{&&,} @code{}, @code{!}


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POSIX @command{bc} does not have the logical operators.


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@item @code{read} function


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POSIX @command{bc} does not have a @code{read} function.


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@item @code{print} statement


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POSIX @command{bc} does not have a @code{print} statement.


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@item @code{continue} statement


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POSIX @command{bc} does not have a continue statement.


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@item array parameters


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POSIX @command{bc} does not (currently) support array parameters in full.


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The POSIX grammar allows for arrays in function definitions, but does


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not provide a method to specify an array as an actual parameter. (This


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is most likely an oversight in the grammar.) Traditional implementations


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of @command{bc} have only call by value array parameters.


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@item function format


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POSIX @command{bc} requires the opening brace on the same line as the


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@code{define} key word and the @code{auto} statement on the next line.


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@item @code{=+}, @code{=}, @code{=*}, @code{=/}, @code{=%}, @code{=^}


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POSIX @command{bc} does not require these "old style" assignment


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operators to be defined. This version may allow these "old style"


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assignments. Use the @code{limits} statement to see if the installed


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version supports them. If it does support the "old style" assignment


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operators, the statement "a = 1" will decrement @code{a} by 1 instead


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of setting @code{a} to the value 1.


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@item spaces in numbers


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Other implementations of @command{bc} allow spaces in numbers. For example,


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"x=1 3" would assign the value 13 to the variable x. The same statement


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would cause a syntax error in this version of @command{bc}.


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@item errors and execution


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This implementation varies from other implementations in terms of what


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code will be executed when syntax and other errors are found in the


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program. If a syntax error is found in a function definition, error


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recovery tries to find the beginning of a statement and continue to


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parse the function. Once a syntax error is found in the function, the


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function will not be callable and becomes undefined.


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Syntax errors in the interactive execution code will invalidate the


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current execution block. The execution block is terminated by an


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end of line that appears after a complete sequence of statements.


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For example,


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@example


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a = 1


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b = 2


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@end example


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has two execution blocks and


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@example


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@{ a = 1


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b = 2 @}


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@end example


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has one execution block. Any runtime error will terminate the execution


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of the current execution block. A runtime warning will not terminate the


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current execution block.


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@item Interrupts


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During an interactive session, the SIGINT signal (usually generated by


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the controlC character from the terminal) will cause execution of the


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current execution block to be interrupted. It will display a "runtime"


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error indicating which function was interrupted. After all runtime


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structures have been cleaned up, a message will be printed to notify the


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user that @command{bc} is ready for more input. All previously defined


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functions remain defined and the value of all nonauto variables are the


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value at the point of interruption. All auto variables and function


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parameters are removed during the clean up process. During a


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noninteractive session, the SIGINT signal will terminate the entire run


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of @command{bc}.


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@end table


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@node Limits, Environment Variables, Comparison with Other Implementations, Top


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@chapter Limits


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The following are the limits currently in place for this @command{bc}


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processor. Some of them may have been changed by an installation. Use


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the @code{limits} statement to see the actual values.


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@table @code


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@item BC_BASE_MAX


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The maximum output base is currently set at 999. The maximum input base


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is 16.


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@item BC_DIM_MAX


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This is currently an arbitrary limit of 65535 as distributed. Your


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installation may be different.


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@item BC_SCALE_MAX


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The number of digits after the decimal point is limited to INT_MAX digits.


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Also, the number of digits before the decimal point is limited to INT_MAX


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digits.


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@item BC_STRING_MAX


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The limit on the number of characters in a string is INT_MAX characters.


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@item exponent


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The value of the exponent in the raise operation (^) is limited to LONG_MAX.


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@item multiply


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The multiply routine may yield incorrect results if a number


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has more than LONG_MAX / 90 total digits. For 32 bit longs, this number is


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23,860,929 digits.


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@item variable names


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The current limit on the number of unique names is 32767 for each of


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simple variables, arrays and functions.


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@end table


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@node Environment Variables, , Limits, Top


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@chapter Environment Variables


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The following environment variables are processed by @command{bc}:


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@table @code


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@item POSIXLY_CORRECT


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This is the same as the s option (@pxref{Command Line Options}).


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@item BC_ENV_ARGS


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This is another mechanism to get arguments to @command{bc}. The format


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is the same as the command line arguments. These arguments are


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processed first, so any files listed in the environment arguments are


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processed before any command line argument files. This allows the user


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to set up "standard" options and files to be processed at every


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invocation of @command{bc}. The files in the environment variables


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would typically contain function definitions for functions the user


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wants defined every time @command{bc} is run.


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@item BC_LINE_LENGTH


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This should be an integer specifying the number of characters in an


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output line for numbers. This includes the backslash and newline


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characters for long numbers. As an extension, the value of zero disables the


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multiline feature. Any other value of this variable that is less than


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3 sets the line length to 70.


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@end table


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@contents


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@bye
