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@settitle bc Command Manual

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@direntry

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

@end direntry

@end ifinfo

@titlepage

@title @command{bc}

@subtitle an arbitrary precision calculator language

@subtitle version @value{BC_VERSION}

@author Philip A. Nelson

@page

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

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

@sp 4

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

51 Franklin Street, Fifth Floor,  Boston, MA 02110-1301  USA.

Permission is granted to make and distribute verbatim copies of

this manual provided the copyright notice and this permission notice

are preserved on all copies.

@ignore

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

results, provided the printed document carries copying permission

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

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

@end ignore

Permission is granted to copy and distribute modified versions of this

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

resulting derived work is distributed under the terms of a permission

notice identical to this one.

Permission is granted to copy and distribute translations of this manual

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

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

by the Foundation.

You may contact the author by:

e-mail: @email{phil@@cs.wwu.edu}@*

us-mail: Philip A. Nelson@*

Computer Science Department, 9062@*

Western Washington University@*

Bellingham, WA 98226-9062

@end titlepage

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

@menu

* Introduction::

* Basic Elements::

* Expressions::

* Statements::

* Functions::

* Examples::

* Readline and Libedit Options::

* Comparison with Other Implementations::

* Limits::

* Environment Variables::

@end menu

@node Introduction, Basic Elements, Top, Top

@chapter Introduction

@menu

* Description::

* Command Line Options::

@end menu

@node Description, Command Line Options, Introduction, Introduction

@section Description

@command{bc} [ -hlwsqv ] [long-options] [ @var{ file ...} ]

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

with interactive execution of statements.  There are some similarities

in the syntax to the C programming language. 

A standard math library is available by command line option.

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

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

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

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

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

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

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

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

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

be rejected.  This document describes the language accepted by this

processor.  Extensions will be identified as such.

The author would like to thank Steve Sommars

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

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

better product due to his involvement.

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

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

@node Command Line Options, Numbers, Description, Introduction

@section Command Line Options

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

@table @code

@item -h, --help

Print the usage and exit.

@item -l, --mathlib

Define the standard math library.

@item -w, --warn

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

@item -s, --standard

Process exactly the POSIX @command{bc} language.

@item -q, --quiet

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

@item -v, --version 

Print the version number and copyright and quit.

@end table

@node Basic Elements, Expressions, Introduction, Top

@chapter Basic Elements

@menu

* Numbers::

* Variables::

* Comments::

@end menu

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

@section Numbers

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

arbitrary precision numbers.  This precision is both in the integer

part and the fractional part.  All numbers are represented internally

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

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

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

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

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

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

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

@node Variables, Comments, Numbers, Basic Elements

@section Variables

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

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

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

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

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

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

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

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

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

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

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

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

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

printed number.  These will be discussed in further detail where

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

as well as used in expressions.

@node Comments, , Variables, Basic Elements

@section Comments

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

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

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

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

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

the start and the end of the comment.

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

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

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

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

@node Expressions, Statements, Basic Elements, Top

@chapter Expressions

@menu 

* About Expressions and Special Variables::

* Basic Expressions::

* Relational Expressions::

* Boolean Expressions::

* Precedence::

* Special Expressions::

@end menu

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

@section About Expressions and Special Variables

The numbers are manipulated by expressions and statements.  Since

the language was designed to be interactive, statements and expressions

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

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

detail later, are defined when encountered.)

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

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

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

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

16 are an extension.)  Assigning a value outside

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

numbers may contain the characters 0-9 and A-Z. (Note: They must be

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

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

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

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

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

3 digit number of the input base.

Full expressions are similar to many other high level languages.

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

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

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

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

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

0 to the maximum number representable by a C integer.

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

@section Basic Expressions

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

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

A simple variable is just a 

@var{name}

and an array variable is specified as 

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

Unless specifically mentioned the scale of the result is the maximum

scale of the expressions involved.

@table @code

@item - expr

The result is the negation of the expression.

@item ++ @var{var}

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

the expression.

@item -- @var{var}

The variable

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

expression.

@item @var{var} ++

 The result of the expression is the value of

the variable and then the variable is incremented by one.

@item @var{var} --

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

the variable is decremented by one.

@item expr + expr

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

@item expr - expr

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

@item expr * expr

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

@item expr / expr

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

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

@item expr % expr

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

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

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

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

to zero and both expressions are integers this expression is the

integer remainder function.

@item expr ^ expr

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

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

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

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

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

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

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

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

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

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

@item ( expr )

This alters the standard precedence to force the evaluation of the

expression.

@item @var{var} = expr

The variable is assigned the value of the expression.

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

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

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

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

@end table

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

@section Relational Expressions

Relational expressions are a special kind of expression that always

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

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

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

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

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

@table @code

@item expr1 < expr2

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

@item expr1 <= expr2

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

@item expr1 > expr2

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

@item expr1 >= expr2

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

@item expr1 == expr2

The result is 1 if expr1 is equal to expr2.

@item expr1 != expr2

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

@end table

@node Boolean Expressions, Precedence, Relational Expressions, Expressions

@section Boolean Expressions

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

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

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

operators are:

@table @code

@item !expr

The result is 1 if expr is 0.

@item expr && expr

The result is 1 if both expressions are non-zero.

@item expr || expr

The result is 1 if either expression is non-zero.

@end table

@node Precedence, Special Expressions, Boolean Expressions, Expressions

@section Precedence

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

@example

|| operator, left associative

&& operator, left associative

! operator, nonassociative

Relational operators, left associative

Assignment operator, right associative

+ and - operators, left associative

*, / and % operators, left associative

^ operator, right associative

unary - operator, nonassociative

++ and -- operators, nonassociative

@end example

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

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

logical operators to have some unusual behavior when used with

assignment expressions.  Consider the expression:

@example

a = 3 < 5

@end example

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

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

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

best to use parentheses when using relational and logical operators

with the assignment operators.

@node Special Expressions, , Precedence, Expressions

@section Special Expressions

There are a few more special expressions that are provided in

@command{bc}.  These have to do with user-defined functions and standard

functions.  They all appear as

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

user-defined functions.  The standard functions are:

@table @code

@item length ( @var{expression} )

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

expression.

@item read ( )

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

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

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

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

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

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

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

variable @var{ibase} for the conversion base.

@item scale ( @var{expression} )

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

decimal point in the expression.

@item sqrt ( @var{expression} )

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

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

generated.

@end table

@node Statements, Functions, Expressions, Top

@chapter Statements

@menu

* Pseudo Statements::

@end menu

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

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

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

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

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

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

newline will cause a syntax error.  Because newlines are statement

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

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

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

series of statements separated by semicolons and newlines.  The

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

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

@table @code

@item @var{expression}

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

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

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

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

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

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

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

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

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

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

@command{bc} uses a multi-character digit method of printing the numbers

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

multi-character digits are separated by spaces.  Each digit contains the

number of characters required to represent the base ten value of

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

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

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

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

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

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

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

without having to retype the expression that printed the number.

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

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

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

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

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

@var{last}.)

@item @var{string}

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

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

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

character is printed after the string.

@item print @var{list}

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

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

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

No terminating newline is printed.  Expressions are evaluated and their

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

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

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

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

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

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

character following the backslash will be ignored.

@item @{ @var{statement_list} @}

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

grouped together for execution.

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

The if statement evaluates the expression and executes statement1 or

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

is non-zero, statement1 is executed.  If statement2 is present and

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

@code{else} clause is an extension.)

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

The while statement will execute the statement while the expression

is non-zero.  It evaluates the expression before each execution of

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

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

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

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

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

evaluated before each execution of the statement.  If it is non-zero,

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

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

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

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

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

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

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

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

statement:

@example

expression1;

while (expression2) @{

   statement;

   expression3;

@}

@end example

@item break

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

statement or @code{for} statement.

@item continue

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

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

@item halt

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

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

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

because the @code{halt} is not executed.

@item return

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

@item return ( @var{expression} )

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

As an extension, the parenthesis are not required.

@end table

@node Pseudo Statements, , Statements, Statements

@section Pseudo Statements

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

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

@table @code

@item limits

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

is an extension.

@item quit

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

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

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

@item warranty

Print a longer warranty notice.  This is an extension.

@end table

@node Functions, Examples, Statements, Top

@chapter Functions

@menu

* Math Library Functions::

@end menu

Functions provide a method of defining a computation that can be

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

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

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

the input.  That definition is then used until another definition

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

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

@example

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

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

@end example

A function call is just an expression of the form

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

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

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

commas.  All parameters  are call by value parameters.

Arrays are specified in the parameter definition by

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

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

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

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

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

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

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

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

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

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

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

same notation as used in parameters.  These variables have their

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

variables are then initialized to zero and used throughout the

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

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

of these variables are restored.  The parameters are really auto

variables that are initialized to a value provided in the function

call.  

Auto variables are different than traditional local variables

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

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

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

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

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

are separated by semicolons or newlines.  Return statements cause the

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

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

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

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

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

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

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

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

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

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

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

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

of @var{ibase} for conversion of numbers.

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

the definition has been slightly relaxed.  The standard requires the

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

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

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

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

@example

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

   define d (n)

       @{ return (2*n); @}

@end example

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

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

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

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

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

session.

@example

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

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

py(1)

--->1<---

0

px(1)

--->1<---

@end example

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

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

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

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

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

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

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

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

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

@node Math Library Functions, , Functions, Functions

@section Math Library Functions

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

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

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

math library defines the following functions:

@table @code

@item s (@var{x})

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

@item c (@var{x})

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

@item a (@var{x})

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

@item l (@var{x})

The natural logarithm of @var{x}.

@item e (@var{x})

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

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

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

@end table

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

@chapter Examples

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

variable @var{pi}.

@example

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

@end example

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

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

@example

scale = 20

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

   When x is small enough, we use the series:

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

*/

define e(x) @{

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

  /* Check the sign of x. */

  if (x<0) @{

    m = 1

    x = -x

  @} 

  /* Precondition x. */

  z = scale;

  scale = 4 + z + .44*x;

  while (x > 1) @{

    f += 1;

    x /= 2;

  @}

  /* Initialize the variables. */

  v = 1+x

  a = x

  d = 1

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

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

    if (e == 0) @{

      if (f>0) while (f--)  v = v*v;

      scale = z

      if (m) return (1/v);

      return (v/1);

    @}

    v += e

  @}

@}

@end example

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

implement a simple program for calculating checkbook balances.  This

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

without having to retype it at every use.

@example

scale=2

print "\nCheck book program\n!"

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

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

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

bal /= 1

print "\n"

while (1) @{

  "current balance = "; bal

  "transaction? "; trans = read()

  if (trans == 0) break;

  bal -= trans

  bal /= 1

@}

quit

@end example

The following is the definition of the recursive factorial function.

@example

define f (x) @{

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

  return (f(x-1) * x);

@}

@end example

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

@chapter Readline and Libedit Options

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

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

library.  This allows the user to do

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

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

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

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

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

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

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

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

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

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

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

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

@chapter Comparison with Other Implementations

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

draft and contains several differences and extensions relative to the

draft and traditional implementations.  It is not implemented in the

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

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

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

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

for debugging the parser and preparing the math library.

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

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

The following is the list of differences and extensions.

@table @asis

@item LANG environment

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

of the LANG environment variable and all environment variables starting

with LC_.

@item names

Traditional and POSIX @command{bc}

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

been extended to be multi-character names that start with a letter and