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This is ../../doc/bc.info, produced by makeinfo version 4.8 from


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../../doc/bc.texi.


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STARTINFODIRENTRY


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


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ENDINFODIRENTRY


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?


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File: bc.info, Node: Top, Next: Introduction, Prev: (dir), Up: (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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?


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File: bc.info, Node: Introduction, Next: Basic Elements, Prev: Top, Up: Top


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1 Introduction


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**************


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* Menu:


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* Description::


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* Command Line Options::


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?


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File: bc.info, Node: Description, Next: Command Line Options, Prev: Introduction, Up: Introduction


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1.1 Description


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===============


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`bc' [ hlwsqv ] [longoptions] [ FILE ... ]


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`bc' is a language that supports arbitrary precision numbers with


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interactive execution of statements. There are some similarities in


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the syntax to the C programming language. A standard math library is


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available by command line option. If requested, the math library is


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defined before processing any files. `bc' starts by processing code


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from all the files listed on the command line in the order listed.


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After all files have been processed, `bc' reads from the standard


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input. All code is executed as it is read. (If a file contains a


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command to halt the processor, `bc' will never read from the standard


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input.)


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This version of `bc' contains several extensions beyond traditional


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`bc' implementations and the POSIX draft standard. Command line


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options can cause these extensions to print a warning or to be


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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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(<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 <bugbc@gnu.org>. Be sure to include the word


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"bc" somewhere in the "Subject:" field.


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?


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File: bc.info, Node: Command Line Options, Next: Numbers, Prev: Description, Up: Introduction


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1.2 Command Line Options


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========================


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`bc' takes the following options from the command line:


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`h, help'


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Print the usage and exit.


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`l, mathlib'


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Define the standard math library.


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`w, warn'


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Give warnings for extensions to POSIX `bc'.


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`s, standard'


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Process exactly the POSIX `bc' language.


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`q, quiet'


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Do not print the normal GNU `bc' welcome.


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`v, version'


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Print the version number and copyright and quit.


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?


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File: bc.info, Node: Basic Elements, Next: Expressions, Prev: Introduction, Up: Top


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2 Basic Elements


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****************


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* Menu:


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* Numbers::


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* Variables::


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* Comments::


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?


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File: bc.info, Node: Numbers, Next: Variables, Prev: Command Line Options, Up: Basic Elements


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2.1 Numbers


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===========


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The most basic element in `bc' is the number. Numbers are arbitrary


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precision numbers. This precision is both in the integer part and the


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fractional part. All numbers are represented internally in decimal and


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all computation is done in decimal. (This version truncates results


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from divide and multiply operations.) There are two attributes of


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numbers, the length and the scale. The length is the total number of


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digits used by `bc' to represent a number and the scale is the total


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number of decimal digits after the decimal point. For example, .000001


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has a length of 6 and scale of 6, while 1935.000 has a length of 7 and


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a scale of 3.


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?


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File: bc.info, Node: Variables, Next: Comments, Prev: Numbers, Up: Basic Elements


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2.2 Variables


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=============


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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 names


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are an extension. In POSIX `bc' all names are a single lower case


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letter.) The type of variable is clear by the context because all


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


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There are four special variables, SCALE, IBASE, OBASE, and LAST.


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SCALE defines how some operations use digits after the decimal point.


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The default value of SCALE is 0. IBASE and OBASE define the conversion


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


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output is base 10. LAST (an extension) is a variable that has the


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value of the last printed number. These will be discussed in further


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detail where appropriate. All of these variables may have values


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assigned to them as well as used in expressions.


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?


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File: bc.info, Node: Comments, Prev: Variables, Up: Basic Elements


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2.3 Comments


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============


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Comments in `bc' start with the characters `/*' and end with the


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characters `*/'. Comments may start anywhere and appear as a single


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


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


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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 `bc', a single line comment has


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been added as an extension. A single line comment starts at a `#'


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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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?


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File: bc.info, Node: Expressions, Next: Statements, Prev: Basic Elements, Up: Top


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3 Expressions


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*************


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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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?


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File: bc.info, Node: About Expressions and Special Variables, Next: Basic Expressions, Prev: Expressions, Up: Expressions


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3.1 About Expressions and Special Variables


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===========================================


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The numbers are manipulated by expressions and statements. Since the


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language was designed to be interactive, statements and expressions are


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


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


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later, are defined when encountered.)


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A simple expression is just a constant. `bc' converts constants into


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


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variable IBASE. (There is an exception in functions.) The legal values


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of IBASE are 2 through 36. (Bases greater than 16 are an extension.)


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Assigning a value outside this range to IBASE will result in a value of


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2 or 36. Input numbers may contain the characters 09 and AZ. (Note:


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They must be capitals. Lower case letters are variable names.) Single


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


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value of IBASE. (i.e. A = 10.) For multidigit numbers, `bc' changes


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all input digits greater or equal to IBASE to the value of IBASE1.


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This makes the number `ZZZ' always be the largest 3 digit number of the


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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 SCALE. Legal values of the variable SCALE are 0 to the maximum


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number representable by a C integer.


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?


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File: bc.info, Node: Basic Expressions, Next: Relational Expressions, Prev: About Expressions and Special Variables, Up: Expressions


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3.2 Basic Expressions


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=====================


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


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complete expression and "VAR" refers to a simple or an array variable.


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A simple variable is just a


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NAME


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and an array variable is specified as


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NAME[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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` expr'


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The result is the negation of the expression.


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`++ VAR'


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


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of the expression.


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` VAR'


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The variable is decremented by one and the new value is the result


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of the expression.


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`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 incremented by one.


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`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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`expr + expr'


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


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`expr  expr'


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The result of the expression is the difference of the two


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expressions.


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`expr * expr'


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


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`expr / expr'


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The result of the expression is the quotient of the two


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expressions. The scale of the result is the value of the variable


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`scale'


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`expr % expr'


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


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in the following way. To compute a%b, first a/b is computed to


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


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scale of the maximum of SCALE+scale(b) and scale(a). If SCALE is


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set to zero and both expressions are integers this expression is


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the integer remainder function.


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`expr ^ expr'


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


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


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second 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 SCALE if the exponent is negative. If the exponent is


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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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SCALE and the scale of the first expression. (e.g. scale(a^b) =


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min(scale(a)*b, max(SCALE, scale(a))).) It should be noted that


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expr^0 will always return the value of 1.


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`( 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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`VAR = expr'


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The variable is assigned the value of the expression.


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`VAR <op>= expr'


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This is equivalent to "VAR = VAR <op> expr" with the exception


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that the "VAR" part is evaluated only once. This can make a


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difference if "VAR" is an array.


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?


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File: bc.info, Node: Relational Expressions, Next: Boolean Expressions, Prev: Basic Expressions, Up: Expressions


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3.3 Relational Expressions


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==========================


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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 `bc' requires


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that relational expressions are used only in `if', `while', and `for'


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statements and that only one relational test may be done in them.) The


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relational operators are


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`expr1 < expr2'


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


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`expr1 <= expr2'


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


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`expr1 > expr2'


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


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`expr1 >= expr2'


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


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`expr1 == expr2'


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The result is 1 if expr1 is equal to expr2.


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`expr1 != expr2'


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


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?


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File: bc.info, Node: Boolean Expressions, Next: Precedence, Prev: Relational Expressions, Up: Expressions


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3.4 Boolean Expressions


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=======================


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Boolean operations are also legal. (POSIX `bc' does NOT have boolean


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


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false and true) as in relational expressions. The boolean operators


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are:


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`!expr'


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The result is 1 if expr is 0.


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`expr && expr'


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The result is 1 if both expressions are nonzero.


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`expr  expr'


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The result is 1 if either expression is nonzero.


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?


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File: bc.info, Node: Precedence, Next: Special Expressions, Prev: Boolean Expressions, Up: Expressions


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3.5 Precedence


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==============


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


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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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This precedence was chosen so that POSIX compliant `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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a = 3 < 5


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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 `bc' is assign


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


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use parentheses when using relational and logical operators with the


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assignment operators.


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?


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File: bc.info, Node: Special Expressions, Prev: Precedence, Up: Expressions


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3.6 Special Expressions


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=======================


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There are a few more special expressions that are provided in `bc'.


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These have to do with userdefined functions and standard functions.


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They all appear as "NAME`('PARAMETERS`)'". *Note Functions::, for


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userdefined functions. The standard functions are:


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`length ( EXPRESSION )'


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The value of the length function is the number of significant


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digits in the expression.


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`read ( )'


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The `read' function (an extension) will read a number from the


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


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


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


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written program that needs input from the user, but never allows


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program code to be input from the user. The value of the `read'


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function is the number read from the standard input using the


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current value of the variable IBASE for the conversion base.


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`scale ( EXPRESSION )'


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The value of the `scale' function is the number of digits after the


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decimal point in the expression.


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`sqrt ( EXPRESSION )'


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The value of the `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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?


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File: bc.info, Node: Statements, Next: Functions, Prev: Expressions, Up: Top


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4 Statements


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************


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* Menu:


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* Pseudo Statements::


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


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expression evaluation. In `bc' statements are executed "as soon as


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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 `bc'. In fact, both a semicolon and a


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newline are used as statement separators. An improperly placed newline


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will cause a syntax error. Because newlines are statement separators,


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it is possible to hide a newline by using the backslash character. The


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sequence "\<nl>", where <nl> is the newline appears to `bc' as


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whitespace instead of a newline. A statement list is a series of


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statements separated by semicolons and newlines. The following is a


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list of `bc' statements and what they do: (Things enclosed in brackets


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( [ ] ) are optional parts of the statement.)


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`EXPRESSION'


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


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


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assignment statement. If the expression is not an assignment


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statement, the expression is evaluated and printed to the output.


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After the number is printed, a newline is printed. For example,


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


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has an embedded assignment. All numbers that are printed are


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printed in the base specified by the variable OBASE. The legal


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values for OBASE are 2 through BC_BASE_MAX (*note Environment


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Variables::). For bases 2 through 16, the usual method of writing


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numbers is used. For bases greater than 16, `bc' uses a


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multicharacter digit method of printing the numbers where each


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


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multicharacter digits are separated by spaces. Each digit


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contains the number of characters required to represent the base


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ten value of "OBASE 1". Since numbers are of arbitrary


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precision, some numbers may not be printable on a single output


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line. These long numbers will be split across lines using the "\"


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as the last character on a line. The maximum number of characters


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printed per line is 70. Due to the interactive nature of `bc',


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printing a number causes the side effect of assigning the printed


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value to the special variable LAST. This allows the user to


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recover the last value printed without having to retype the


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expression that printed the number. Assigning to LAST is legal


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and will overwrite the last printed value with the assigned value.


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The newly assigned value will remain until the next number is


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printed or another value is assigned to LAST. (Some installations


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may allow the use of a single period (.) which is not part of a


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number as a short hand notation for for LAST.)


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`STRING'


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


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quote character and contain all characters until the next double


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quote character. All characters are taken literally, including


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any newline. No newline character is printed after the string.


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`print LIST'


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The `print' statement (an extension) provides another method of


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output. The 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


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list. No terminating newline is printed. Expressions are


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evaluated and their value is printed and assigned to the variable


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`last'. Strings in the print statement are printed to the output


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and may contain special characters. Special characters start with


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the backslash character (\e). The special characters recognized


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by `bc' are "a" (alert or bell), "b" (backspace), "f" (form feed),


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"n" (newline), "r" (carriage return), "q" (double quote), "t"


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(tab), and "\e" (backslash). Any other character following the


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backslash will be ignored.


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`{ STATEMENT_LIST }'


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This is the compound statement. It allows multiple statements to


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be grouped together for execution.


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`if ( EXPRESSION ) STATEMENT1 [else STATEMENT2]'


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The if statement evaluates the expression and executes statement1


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


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expression is nonzero, statement1 is executed. If statement2 is


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present and the value of the expression is 0, then statement2 is


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executed. (The `else' clause is an extension.)


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`while ( EXPRESSION ) 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 `break' statement.


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`for ( [EXPRESSION1] ; [EXPRESSION2] ; [EXPRESSION3] ) STATEMENT'


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The `for' statement controls repeated execution of the statement.


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EXPRESSION1 is evaluated before the loop. EXPRESSION2 is


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evaluated before each execution of the statement. If it is


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


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terminated. After each execution of the statement, EXPRESSION3 is


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evaluated before the reevaluation of expression2. If EXPRESSION1


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or EXPRESSION3 are missing, nothing is evaluated at the point they


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would be evaluated. If EXPRESSION2 is missing, it is the same as


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substituting the value 1 for EXPRESSION2. (The optional


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expressions are an extension. POSIX `bc' requires all three


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expressions.) The following is equivalent code for the `for'


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statement:


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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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`break'


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This statement causes a forced exit of the most recent enclosing


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`while' statement or `for' statement.


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`continue'


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The `continue' statement (an extension) causes the most recent


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enclosing `for' statement to start the next iteration.


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`halt'


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The `halt' statement (an extension) is an executed statement that


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causes the `bc' processor to quit only when it is executed. For


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example, "if (0 == 1) halt" will not cause `bc' to terminate


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because the `halt' is not executed.


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`return'


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Return the value 0 from a function. (*Note Functions::.)


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`return ( EXPRESSION )'


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Return the value of the expression from a function. (*Note


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Functions::.) As an extension, the parenthesis are not required.


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?


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File: bc.info, Node: Pseudo Statements, Prev: Statements, Up: Statements


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4.1 Pseudo Statements


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=====================


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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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`limits'


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Print the local limits enforced by the local version of `bc'. This


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is an extension.


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`quit'


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When the `quit' statement is read, the `bc' processor is


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terminated, regardless of where the `quit' statement is found. For


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example, "if (0 == 1) quit" will cause `bc' to terminate.


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`warranty'


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Print a longer warranty notice. This is an extension.


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?


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File: bc.info, Node: Functions, Next: Examples, Prev: Statements, Up: Top


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5 Functions


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***********


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70b277 


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* Menu:


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* Math Library Functions::


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Functions provide a method of defining a computation that can be


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executed later. Functions in `bc' always compute a value and return it


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to the caller. Function definitions are "dynamic" in the sense that a


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function is undefined until a definition is encountered in the input.


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That definition is then used until another definition function for the


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same name is encountered. The new definition then replaces the older


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definition. A function is defined as follows:


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`define' NAME `(' PARAMETERS `)' `{' NEWLINE


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AUTO_LIST STATEMENT_LIST `}'


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70b277 


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A function call is just an expression of the form "`name'


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`('PARAMETERS`)'".


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


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definition, zero or more parameters are defined by listing their names


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separated by commas. All parameters are call by value parameters.


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Arrays are specified in the parameter definition by the notation


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"NAME`[ ]'". In the function call, actual parameters are full


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expressions for number parameters. The same notation is used for


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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


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dynamic, parameter numbers and types are checked when a function is


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called. Any mismatch in number or types of parameters will cause a


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


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undefined function.


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The AUTO_LIST is an optional list of variables that are for "local"


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use. The syntax of the auto list (if present) is "`auto' NAME, ... ;".


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(The semicolon is optional.) Each NAME is the name of an auto


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variable. Arrays may be specified by using the same notation as used


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in parameters. These variables have their values pushed onto a stack


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at the start of the function. The variables are then initialized to


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zero and used throughout the execution of the function. At function


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exit, these variables are popped so that the original value (at the


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time of the function call) of these variables are restored. The


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parameters are really auto variables that are initialized to a value


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provided in the function call. Auto variables are different than


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traditional local variables because if function A calls function B, B


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may access function A's auto variables by just using the same name,


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unless function B has called them auto variables. Due to the fact that


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auto variables and parameters are pushed onto a stack, `bc' supports


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recursive functions.


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70b277 


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The function body is a list of `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, "`return'", returns


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the value 0 to the calling expression. The second form, "`return' (


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EXPRESSION )", computes the value of the expression and returns that


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value to the calling expression. There is an implied "`return' (0)" at


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the end of every function. This allows a function to terminate and


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return 0 without an explicit `return' statement.


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70b277 


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Functions also change the usage of the variable IBASE. All


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


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IBASE at the time of the function call. Changes of IBASE will be


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ignored during the execution of the function except for the standard


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function `read', which will always use the current value of IBASE for


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conversion of numbers.


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70b277 


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


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of the definition has been slightly relaxed. The standard requires the


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opening brace be on the same line as the `define' keyword and all other


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parts must be on following lines. This version of `bc' will allow any


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number of newlines before and after the opening brace of the function.


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For example, the following definitions are legal.


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70b277 


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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 


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Functions may be defined as `void'. A void funtion returns no value


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and thus may not be used in any place that needs a value. A void


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function does not produce any output when called by itself on an input


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line. The key word `void' is placed between the key word `define' and


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the function name. For example, consider the following session.


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70b277 


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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 


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Since `py' is not a void function, the call of `py(1)' prints the


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


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


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return statement is zero, the zero is printed. For `px(1)', no zero is


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printed because the function is a void function.


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70b277 


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


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variable array, the declaration of the array parameter in the function


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definition looks like "`*'NAME`[]'". The call to the function remains


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the same as call by value arrays.


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?


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File: bc.info, Node: Math Library Functions, Prev: Functions, Up: Functions


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5.1 Math Library Functions


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==========================


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70b277 


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If `bc' is invoked with the `l' option, a math library is preloaded


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and the default SCALE is set to 20. The math functions will calculate


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


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library defines the following functions:


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`s (X)'


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The sine of X, X is in radians.


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`c (X)'


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The cosine of X, X is in radians.


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70b277 


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`a (X)'


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The arctangent of X, arctangent returns radians.


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`l (X)'


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The natural logarithm of X.


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70b277 


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`e (X)'


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The exponential function of raising E to the value X.


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70b277 


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`j (N, X)'


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The Bessel function of integer order N of X.


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70b277 


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?


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File: bc.info, Node: Examples, Next: Readline and Libedit Options, Prev: Functions, Up: Top


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6 Examples


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70b277 
**********


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70b277 


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


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variable PI.


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70b277 


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


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70b277 


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


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the math library. This function is written in POSIX `bc'.


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70b277 


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70b277 


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scale = 20


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70b277 


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


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When x is small enough, we use the series:


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


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*/


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70b277 


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define e(x) {


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


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70b277 


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/* Check the sign of x. */


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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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/* 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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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 
}


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70b277 


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70b277 
The following is code that uses the extended features of `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 


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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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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


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70b277 


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


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70b277 


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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 
}


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70b277 


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70b277 
?


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70b277 
File: bc.info, Node: Readline and Libedit Options, Next: Comparison with Other Implementations, Prev: Examples, Up: Top


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70b277 


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7 Readline and Libedit Options


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******************************


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70b277 


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GNU `bc' can be compiled (via a configure option) to use the GNU


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`readline' input editor library or the BSD `libedit' library. This


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allows the user to do more editing of lines before sending them to


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`bc'. It also allows for a history of previous lines typed. When this


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option is selected, `bc' has one more special variable. This special


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70b277 
variable, HISTORY is the number of lines of history retained. A value


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of 1 means that an unlimited number of history lines are retained.


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70b277 
This is the default value. Setting the value of HISTORY to a positive


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number restricts the number of history lines to the number given. The


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value of 0 disables the history feature. For more information, read


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70b277 
the user manuals for the GNU `readline', `history' and BSD `libedit'


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70b277 
libraries. One can not enable both `readline' and `libedit' at the


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70b277 
same time.


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70b277 


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70b277 
?


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70b277 
File: bc.info, Node: Comparison with Other Implementations, Next: Limits, Prev: Readline and Libedit Options, Up: Top


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70b277 


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8 Comparison with Other Implementations


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***************************************


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70b277 


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This version of `bc' was implemented from the POSIX P1003.2/D11 draft


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70b277 
and contains several differences and extensions relative to the draft


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70b277 
and traditional implementations. It is not implemented in the


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70b277 
traditional way using `dc'. This version is a single process which


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70b277 
parses and runs a byte code translation of the program. There is an


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


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70b277 
code to the standard output instead of running it. It was mainly used


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70b277 
for debugging the parser and preparing the math library.


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70b277 


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70b277 
A major source of differences is extensions, where a feature is


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extended to add more functionality and additions, where new features


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70b277 
are added. The following is the list of differences and extensions.


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70b277 


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70b277 
LANG environment


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70b277 
This version does not conform to the POSIX standard in the


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70b277 
processing of the LANG environment variable and all environment


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70b277 
variables starting with LC_.


Packit 
70b277 


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70b277 
names


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70b277 
Traditional and POSIX `bc' have single letter names for functions,


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70b277 
variables and arrays. They have been extended to be


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70b277 
multicharacter names that start with a letter and may contain


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70b277 
letters, numbers and the underscore character.


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70b277 


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70b277 
Strings


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70b277 
Strings are not allowed to contain NUL characters. POSIX says all


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characters must be included in strings.


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70b277 


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70b277 
last


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70b277 
POSIX `bc' does not have a \fBlast variable. Some implementations


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70b277 
of `bc' use the period (.) in a similar way.


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70b277 


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comparisons


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70b277 
POSIX `bc' allows comparisons only in the `if' statement, the


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`while' statement, and the second expression of the `for'


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70b277 
statement. Also, only one relational operation is allowed in each


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70b277 
of those statements.


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70b277 


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70b277 
`if' statement, `else' clause


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70b277 
POSIX `bc' does not have an `else' clause.


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70b277 


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70b277 
`for' statement


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POSIX `bc' requires all expressions to be present in the `for'


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statement.


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`&&,' `', `!'


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POSIX `bc' does not have the logical operators.


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`read' function


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POSIX `bc' does not have a `read' function.


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`print' statement


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POSIX `bc' does not have a `print' statement.


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`continue' statement


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POSIX `bc' does not have a continue statement.


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array parameters


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POSIX `bc' does not (currently) support array parameters in full.


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The POSIX grammar allows for arrays in function definitions, but


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does not provide a method to specify an array as an actual


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parameter. (This is most likely an oversight in the grammar.)


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Traditional implementations of `bc' have only call by value array


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parameters.


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function format


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POSIX `bc' requires the opening brace on the same line as the


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`define' key word and the `auto' statement on the next line.


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`=+', `=', `=*', `=/', `=%', `=^'


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POSIX `bc' does not require these "old style" assignment operators


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


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assignments. Use the `limits' statement to see if the installed


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


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assignment operators, the statement "a = 1" will decrement `a' by


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1 instead of setting `a' to the value 1.


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spaces in numbers


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Other implementations of `bc' allow spaces in numbers. For


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example, "x=1 3" would assign the value 13 to the variable x. The


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same statement would cause a syntax error in this version of `bc'.


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errors and execution


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This implementation varies from other implementations in terms of


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what code will be executed when syntax and other errors are found


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in the program. If a syntax error is found in a function


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definition, error recovery tries to find the beginning of a


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statement and continue to parse the function. Once a syntax error


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is found in the function, the function will not be callable and


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becomes undefined. Syntax errors in the interactive execution


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code will invalidate the current execution block. The execution


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block is terminated by an end of line that appears after a


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complete sequence of statements. For example,


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a = 1


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b = 2


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has two execution blocks and


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{ a = 1


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b = 2 }


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has one execution block. Any runtime error will terminate the


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execution of the current execution block. A runtime warning will


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not terminate the current execution block.


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Interrupts


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During an interactive session, the SIGINT signal (usually


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generated by the controlC character from the terminal) will cause


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execution of the current execution block to be interrupted. It


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will display a "runtime" error indicating which function was


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interrupted. After all runtime structures have been cleaned up, a


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message will be printed to notify the user that `bc' is ready for


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more input. All previously defined functions remain defined and


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the value of all nonauto variables are the value at the point of


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interruption. All auto variables and function parameters are


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removed during the clean up process. During a noninteractive


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session, the SIGINT signal will terminate the entire run of `bc'.


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?


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File: bc.info, Node: Limits, Next: Environment Variables, Prev: Comparison with Other Implementations, Up: Top


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9 Limits


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********


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The following are the limits currently in place for this `bc'


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


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the `limits' statement to see the actual values.


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`BC_BASE_MAX'


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


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input base is 16.


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`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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`BC_SCALE_MAX'


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


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digits. Also, the number of digits before the decimal point is


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limited to INT_MAX digits.


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`BC_STRING_MAX'


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


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characters.


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`exponent'


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


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LONG_MAX.


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`multiply'


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The multiply routine may yield incorrect results if a number has


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


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number is 23,860,929 digits.


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`variable names'


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


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of simple variables, arrays and functions.


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?


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File: bc.info, Node: Environment Variables, Prev: Limits, Up: Top


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10 Environment Variables


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************************


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The following environment variables are processed by `bc':


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`POSIXLY_CORRECT'


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This is the same as the s option (*note Command Line Options::).


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`BC_ENV_ARGS'


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This is another mechanism to get arguments to `bc'. The format is


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the same as the command line arguments. These arguments are


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processed first, so any files listed in the environment arguments


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are processed before any command line argument files. This allows


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the user to set up "standard" options and files to be processed at


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every invocation of `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 `bc' is run.


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`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


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disables the multiline feature. Any other value of this variable


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that is less than 3 sets the line length to 70.


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?


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Tag Table:


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Node: Top201


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Node: Introduction493


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Node: Description658


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Node: Command Line Options2117


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Node: Basic Elements2687


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Node: Numbers2862


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Node: Variables3633


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Node: Comments4747


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Node: Expressions5493


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Node: About Expressions and Special Variables5777


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Node: Basic Expressions7560


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Node: Relational Expressions10506


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Node: Boolean Expressions11516


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Node: Precedence12076


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Node: Special Expressions13241


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Node: Statements14628


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Node: Pseudo Statements21261


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Node: Functions21914


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Node: Math Library Functions27077


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Node: Examples27793


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Node: Readline and Libedit Options29777


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Node: Comparison with Other Implementations30808


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Node: Limits36090


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Node: Environment Variables37347


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?


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End Tag Table
