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- Committer: Bazaar Package Importer
- Author(s): Dirk Eddelbuettel
- Date: 2002-04-13 11:33:49 UTC
- Revision ID: james.westby@ubuntu.com-20020413113349-hl2r1t730b91ov68
Tags: upstream-1.06
Import upstream version 1.06
- files added:
- Examples
- Test
- bc
- dc
- doc
- h
- lib
added
removed
doc/bc.texi
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\input texinfo @c -*-texinfo-*-
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@c %**start of header
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@setfilename bc.info
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@settitle bc Command Manual
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@c %**end of header
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@c This file has the new style title page commands.
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@c Run `makeinfo' rather than `texinfo-format-buffer'.
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@smallbook
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@c tex
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@c \overfullrule=0pt
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@c end tex
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@titlepage
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@title @command{bc}
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@subtitle an arbitrary precision calculator language
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@subtitle version 1.06
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@author Philip A. Nelson
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@page
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This manual documents @command{bc}, an arbitrary precision calculator language.
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This manual is part of GNU @command{bc}.@*
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@sp4
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Copyright (C) 1991, 1992, 1993, 1994, 1997 Free Software Foundation, Inc.
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59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
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Permission is granted to make and distribute verbatim copies of
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this manual provided the copyright notice and this permission notice
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are preserved on all copies.
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@iftex
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Permission is granted to process this file through TeX and print the
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results, provided the printed document carries copying permission
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notice identical to this one except for the removal of this paragraph
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(this paragraph not being relevant to the printed manual).
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@end iftex
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided that the entire
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resulting derived work is distributed under the terms of a permission
45
notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
48
into another language, under the above conditions for modified versions,
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except that this permission notice may be stated in a translation approved
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by the Foundation.
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You may contact the author by:
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e-mail: @email{phil@@cs.wwu.edu}@*
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us-mail: Philip A. Nelson@*
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Computer Science Department, 9062@*
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Western Washington University@*
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Bellingham, WA 98226-9062
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@end titlepage
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@node Top, Introduction, (dir), (dir)
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@menu
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* Introduction::
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* Basic Elements::
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* Expressions::
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* Statements::
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* Functions::
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* Examples::
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* Readline and Libedit Options::
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* GNU @command{bc} and Other Implementations::
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* Limits::
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* Environment Variables::
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@end menu
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@node Introduction, Basic Elements, Top, Top
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@chapter Introduction
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@menu
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* Description::
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* Command Line Options::
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@end menu
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@node Description, Command Line Options, Introduction, Introduction
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@section Description
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@command{bc} [ -hlwsqv ] [long-options] [ @var{ file ...} ]
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@command{bc} is a language that supports arbitrary precision numbers
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with interactive execution of statements. There are some similarities
90
in the syntax to the C programming language.
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A standard math library is available by command line option.
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If requested, the math library is defined before processing any files.
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@command{bc} starts by processing code from all the files listed
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on the command line in the order listed. After all files have been
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processed, @command{bc} reads from the standard input. All code is
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executed as it is read. (If a file contains a command to halt the
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processor, @command{bc} will never read from the standard input.)
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This version of @command{bc} contains several extensions beyond
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traditional @command{bc} implementations and the POSIX draft standard.
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Command line options can cause these extensions to print a warning or to
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be rejected. This document describes the language accepted by this
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processor. Extensions will be identified as such.
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The author would like to thank Steve Sommars
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(@email{Steve.Sommars@@att.com}) for his extensive help in testing the
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implementation. Many great suggestions were given. This is a much
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better product due to his involvement.
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Email bug reports to @email{bug-bc@@gnu.org}. Be sure to include
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the word ``bc'' somewhere in the ``Subject:'' field.
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@node Command Line Options, Numbers, Description, Introduction
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@section Command Line Options
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@command{bc} takes the following options from the command line:
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@table @code
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@item -h, --help
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Print the usage and exit.
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@item -l, --mathlib
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Define the standard math library.
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@item -w, --warn
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Give warnings for extensions to POSIX @command{bc}.
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@item -s, --standard
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Process exactly the POSIX @command{bc} language.
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@item -q, --quiet
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Do not print the normal GNU @command{bc} welcome.
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@item -v, --version
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Print the version number and copyright and quit.
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@end table
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@node Basic Elements, Expressions, Introduction, Top
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@chapter Basic Elements
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@menu
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* Numbers::
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* Variables::
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* Comments::
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@end menu
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@node Numbers, Variables, Command Line Options, Basic Elements
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@section Numbers
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The most basic element in @command{bc} is the number. Numbers are
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arbitrary precision numbers. This precision is both in the integer part
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and the fractional part. All numbers are represented internally in
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decimal and all computation is done in decimal. (This version truncates
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results from divide and multiply operations.) There are two attributes
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of numbers, the length and the scale. The length is the total number of
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significant decimal digits in a number and the scale is the total number
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of decimal digits after the decimal point. For example, .000001 has a
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length of 6 and scale of 6, while 1935.000 has a length of 7 and a scale
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of 3.
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@node Variables, Comments, Numbers, Basic Elements
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@section Variables
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Numbers are stored in two types of variables, simple variables and
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arrays. Both simple variables and array variables are named. Names
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begin with a letter followed by any number of letters, digits and
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underscores. All letters must be lower case. (Full alphanumeric
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names are an extension. In POSIX @command{bc} all names are a single
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lower case letter.) The type of variable is clear by the context
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because all array variable names will be followed by brackets ( [ ] ).
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There are four special variables, @var{scale}, @var{ibase}, @var{obase}, and
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@var{last}. @var{scale} defines how some operations use digits after the
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decimal point. The default value of @var{scale} is 0. @var{ibase}
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and @var{obase} define the conversion base for input and output
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numbers. The default for both input and output is base 10.
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@var{last} (an extension) is a variable that has the value of the last
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printed number. These will be discussed in further detail where
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appropriate. All of these variables may have values assigned to them
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as well as used in expressions.
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@node Comments, , Variables, Basic Elements
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@section Comments
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Comments in @command{bc} start with the characters @code{/*} and end with
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the characters @code{*/}. Comments may start anywhere and appear as a
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single space in the input. (This causes comments to delimit other
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input items. For example, a comment can not be found in the middle of
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a variable name.) Comments include any newlines (end of line) between
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the start and the end of the comment.
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To support the use of scripts for @command{bc}, a single line comment has been
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added as an extension. A single line comment starts at a @code{#}
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character and continues to the next end of the line. The end of line
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character is not part of the comment and is processed normally.
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@node Expressions, Statements, Basic Elements, Top
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@chapter Expressions
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@menu
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* About Expressions and Special Variables::
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* Basic Expressions::
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* Relational Expressions::
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* Boolean Expressions::
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* Precedence::
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* Special Expressions::
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@end menu
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@node About Expressions and Special Variables, Basic Expressions, Expressions, Expressions
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@section About Expressions and Special Variables
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The numbers are manipulated by expressions and statements. Since
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the language was designed to be interactive, statements and expressions
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are executed as soon as possible. There is no main program. Instead,
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code is executed as it is encountered. (Functions, discussed in
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detail later, are defined when encountered.)
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219
A simple expression is just a constant. @command{bc} converts constants
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into internal decimal numbers using the current input base, specified by
221
the variable @var{ibase}. (There is an exception in functions.) The
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legal values of @var{ibase} are 2 through 16. Assigning a value outside
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this range to @var{ibase} will result in a value of 2 or 16. Input
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numbers may contain the characters 0-9 and A-F. (Note: They must be
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capitals. Lower case letters are variable names.) Single digit numbers
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always have the value of the digit regardless of the value of
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@var{ibase}. (i.e. A = 10.) For multi-digit numbers, @command{bc}
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changes all input digits greater or equal to @var{ibase} to the value of
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@var{ibase}-1. This makes the number @code{FFF} always be the largest
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3 digit number of the input base.
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Full expressions are similar to many other high level languages.
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Since there is only one kind of number, there are no rules for mixing
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types. Instead, there are rules on the scale of expressions. Every
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expression has a scale. This is derived from the scale of original
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numbers, the operation performed and in many cases, the value of the
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variable @var{scale}. Legal values of the variable @var{scale} are
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0 to the maximum number representable by a C integer.
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@node Basic Expressions, Relational Expressions, About Expressions and Special Variables, Expressions
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@section Basic Expressions
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In the following descriptions of legal expressions, "expr" refers to a
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complete expression and "@var{var}" refers to a simple or an array variable.
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A simple variable is just a
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@var{name}
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and an array variable is specified as
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@var{name}[@var{expr}]
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Unless specifically mentioned the scale of the result is the maximum
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scale of the expressions involved.
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@table @code
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@item - expr
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The result is the negation of the expression.
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@item ++ @var{var}
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The variable is incremented by one and the new value is the result of
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the expression.
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@item -- @var{var}
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The variable
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is decremented by one and the new value is the result of the
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expression.
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@item @var{var} ++
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The result of the expression is the value of
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the variable and then the variable is incremented by one.
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@item @var{var} --
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The result of the expression is the value of the variable and then
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the variable is decremented by one.
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@item expr + expr
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The result of the expression is the sum of the two expressions.
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@item expr - expr
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The result of the expression is the difference of the two expressions.
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@item expr * expr
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The result of the expression is the product of the two expressions.
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@item expr / expr
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The result of the expression is the quotient of the two expressions.
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The scale of the result is the value of the variable @code{scale}
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@item expr % expr
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The result of the expression is the "remainder" and it is computed in the
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following way. To compute a%b, first a/b is computed to @var{scale}
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digits. That result is used to compute a-(a/b)*b to the scale of the
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maximum of @var{scale}+scale(b) and scale(a). If @var{scale} is set
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to zero and both expressions are integers this expression is the
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integer remainder function.
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@item expr ^ expr
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The result of the expression is the value of the first raised to the
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second. The second expression must be an integer. (If the second
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expression is not an integer, a warning is generated and the
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expression is truncated to get an integer value.) The scale of the
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result is @var{scale} if the exponent is negative. If the exponent
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is positive the scale of the result is the minimum of the scale of the
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first expression times the value of the exponent and the maximum of
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@var{scale} and the scale of the first expression. (e.g. scale(a^b)
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= min(scale(a)*b, max(@var{scale}, scale(a))).) It should be noted
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that expr^0 will always return the value of 1.
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@item ( expr )
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This alters the standard precedence to force the evaluation of the
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expression.
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@item @var{var} = expr
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The variable is assigned the value of the expression.
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@item @var{var} <op>= expr
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This is equivalent to "@var{var} = @var{var} <op> expr" with the
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exception that the "@var{var}" part is evaluated only once. This can
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make a difference if "@var{var}" is an array.
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@end table
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@node Relational Expressions, Boolean Expressions, Basic Expressions, Expressions
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@section Relational Expressions
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Relational expressions are a special kind of expression that always
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evaluate to 0 or 1, 0 if the relation is false and 1 if the relation is
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true. These may appear in any legal expression. (POSIX @command{bc}
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requires that relational expressions are used only in @code{if},
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@code{while}, and @code{for} statements and that only one relational
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test may be done in them.) The relational operators are
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@table @code
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@item expr1 < expr2
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The result is 1 if expr1 is strictly less than expr2.
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@item expr1 <= expr2
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The result is 1 if expr1 is less than or equal to expr2.
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@item expr1 > expr2
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The result is 1 if expr1 is strictly greater than expr2.
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@item expr1 >= expr2
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The result is 1 if expr1 is greater than or equal to expr2.
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@item expr1 == expr2
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The result is 1 if expr1 is equal to expr2.
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@item expr1 != expr2
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The result is 1 if expr1 is not equal to expr2.
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@end table
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@node Boolean Expressions, Precedence, Relational Expressions, Expressions
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@section Boolean Expressions
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Boolean operations are also legal. (POSIX @command{bc} does NOT have
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boolean operations). The result of all boolean operations are 0 and 1
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(for false and true) as in relational expressions. The boolean
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operators are:
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@table @code
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@item !expr
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The result is 1 if expr is 0.
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@item expr && expr
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The result is 1 if both expressions are non-zero.
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@item expr || expr
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The result is 1 if either expression is non-zero.
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@end table
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@node Precedence, Special Expressions, Boolean Expressions, Expressions
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@section Precedence
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The expression precedence is as follows: (lowest to highest)
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@example
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|| operator, left associative
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&& operator, left associative
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! operator, nonassociative
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Relational operators, left associative
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Assignment operator, right associative
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+ and - operators, left associative
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*, / and % operators, left associative
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^ operator, right associative
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unary - operator, nonassociative
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@end example
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This precedence was chosen so that POSIX compliant @command{bc} programs
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will run correctly. This will cause the use of the relational and
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logical operators to have some unusual behavior when used with
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assignment expressions. Consider the expression:
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@example
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a = 3 < 5
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@end example
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Most C programmers would assume this would assign the result of "3 <
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5" (the value 1) to the variable "a". What this does in @command{bc} is
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assign the value 3 to the variable "a" and then compare 3 to 5. It is
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best to use parentheses when using relational and logical operators
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with the assignment operators.
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@node Special Expressions, , Precedence, Expressions
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@section Special Expressions
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There are a few more special expressions that are provided in
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@command{bc}. These have to do with user-defined functions and standard
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functions. They all appear as
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"@var{name}@code{(}@var{parameters}@code{)}". @xref{Functions}, for
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user-defined functions. The standard functions are:
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@table @code
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@item length ( expression )
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The value of the length function is the number of significant digits in the
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expression.
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@item read ( )
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The @code{read} function (an extension) will read a number from the
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standard input, regardless of where the function occurs. Beware, this
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can cause problems with the mixing of data and program in the standard
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input. The best use for this function is in a previously written
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program that needs input from the user, but never allows program code to
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be input from the user. The value of the @code{read} function is the
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number read from the standard input using the current value of the
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variable @var{ibase} for the conversion base.
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@item scale ( expression )
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The value of the @code{scale} function is the number of digits after the
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decimal point in the expression.
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@item sqrt ( expression )
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The value of the @code{sqrt} function is the square root of the
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expression. If the expression is negative, a run time error is
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generated.
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@end table
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@node Statements, Functions, Expressions, Top
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@chapter Statements
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@menu
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* Pseudo Statements::
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@end menu
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Statements (as in most algebraic languages) provide the sequencing of
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expression evaluation. In @command{bc} statements are executed "as soon
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as possible." Execution happens when a newline in encountered and there
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is one or more complete statements. Due to this immediate execution,
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newlines are very important in @command{bc}. In fact, both a semicolon
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and a newline are used as statement separators. An improperly placed
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newline will cause a syntax error. Because newlines are statement
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separators, it is possible to hide a newline by using the backslash
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character. The sequence "\<nl>", where <nl> is the newline appears to
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@command{bc} as whitespace instead of a newline. A statement list is a
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series of statements separated by semicolons and newlines. The
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following is a list of @command{bc} statements and what they do: (Things
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enclosed in brackets ( [ ] ) are optional parts of the statement.)
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@table @var
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@item expression
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This statement does one of two things. If the expression starts with
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"<variable> <assignment> ...", it is considered to be an assignment
463
statement. If the expression is not an assignment statement, the
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expression is evaluated and printed to the output. After the number is
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printed, a newline is printed. For example, "a=1" is an assignment
466
statement and "(a=1)" is an expression that has an embedded assignment.
467
All numbers that are printed are printed in the base specified by the
468
variable @var{obase}. The legal values for @var{obase} are 2 through
469
BC_BASE_MAX (@pxref{Environment Variables}). For bases 2 through 16,
470
the usual method of writing numbers is used. For bases greater than 16,
471
@command{bc} uses a multi-character digit method of printing the numbers
472
where each higher base digit is printed as a base 10 number. The
473
multi-character digits are separated by spaces. Each digit contains the
474
number of characters required to represent the base ten value of
475
"@var{obase} -1". Since numbers are of arbitrary precision, some
476
numbers may not be printable on a single output line. These long
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numbers will be split across lines using the "\" as the last character
478
on a line. The maximum number of characters printed per line is 70.
479
Due to the interactive nature of @command{bc}, printing a number causes
480
the side effect of assigning the printed value to the special variable
481
@var{last}. This allows the user to recover the last value printed
482
without having to retype the expression that printed the number.
483
Assigning to @var{last} is legal and will overwrite the last printed
484
value with the assigned value. The newly assigned value will remain
485
until the next number is printed or another value is assigned to
486
@var{last}. (Some installations may allow the use of a single period
487
(.) which is not part of a number as a short hand notation for for
488
@var{last}.)
489
490
@item string
491
The string is printed to the output. Strings start with a double quote
492
character and contain all characters until the next double quote character.
493
All characters are taken literally, including any newline. No newline
494
character is printed after the string.
495
496
@item @code{print} @var{list}
497
The @code{print} statement (an extension) provides another method of
498
output. The @var{list} is a list of strings and expressions separated by
499
commas. Each string or expression is printed in the order of the list.
500
No terminating newline is printed. Expressions are evaluated and their
501
value is printed and assigned to the variable @code{last}. Strings in
502
the print statement are printed to the output and may contain special
503
characters. Special characters start with the backslash character (\e).
504
The special characters recognized by @command{bc} are "a" (alert or
505
bell), "b" (backspace), "f" (form feed), "n" (newline), "r" (carriage
506
return), "q" (double quote), "t" (tab), and "\e" (backslash). Any other
507
character following the backslash will be ignored.
508
509
@item @{ statement_list @}
510
This is the compound statement. It allows multiple statements to be
511
grouped together for execution.
512
513
@item @code{if} ( expression ) statement1 [@code{else} statement2]
514
The if statement evaluates the expression and executes statement1 or
515
statement2 depending on the value of the expression. If the expression
516
is non-zero, statement1 is executed. If statement2 is present and
517
the value of the expression is 0, then statement2 is executed. (The
518
@code{else} clause is an extension.)
519
520
@item @code{while} ( expression ) statement
521
The while statement will execute the statement while the expression
522
is non-zero. It evaluates the expression before each execution of
523
the statement. Termination of the loop is caused by a zero
524
expression value or the execution of a @code{break} statement.
525
526
@item @code{for} ( [expression1] ; [expression2] ; [expression3] ) statement
527
The @code{for} statement controls repeated execution of the statement.
528
@var{Expression1} is evaluated before the loop. @var{Expression2} is
529
evaluated before each execution of the statement. If it is non-zero,
530
the statement is evaluated. If it is zero, the loop is terminated.
531
After each execution of the statement, @var{expression3} is evaluated
532
before the reevaluation of expression2. If @var{expression1} or
533
@var{expression3} are missing, nothing is evaluated at the point they
534
would be evaluated. If @var{expression2} is missing, it is the same as
535
substituting the value 1 for @var{expression2}. (The optional
536
expressions are an extension. POSIX @command{bc} requires all three
537
expressions.) The following is equivalent code for the @code{for}
538
statement:
539
540
@example
541
expression1;
542
while (expression2) @{
543
statement;
544
expression3;
545
@}
546
@end example
547
548
@item @code{break}
549
This statement causes a forced exit of the most recent enclosing @code{while}
550
statement or @code{for} statement.
551
552
@item @code{continue}
553
The @code{continue} statement (an extension) causes the most recent enclosing
554
@code{for} statement to start the next iteration.
555
556
@item @code{halt}
557
The @code{halt} statement (an extension) is an executed statement that
558
causes the @command{bc} processor to quit only when it is executed. For
559
example, "if (0 == 1) halt" will not cause @command{bc} to terminate
560
because the @code{halt} is not executed.
561
562
@item @code{return}
563
Return the value 0 from a function. (@xref{Functions}.)
564
565
@item @code{return} ( expression )
566
Return the value of the expression from a function. (@xref{Functions}.)
567
As an extension, the parenthesis are not required.
568
@end table
569
570
@node Pseudo Statements, , Statements, Statements
571
@section Pseudo Statements
572
573
These statements are not statements in the traditional sense. They are
574
not executed statements. Their function is performed at "compile" time.
575
576
@table @code
577
@item limits
578
Print the local limits enforced by the local version of @command{bc}. This
579
is an extension.
580
581
@item quit
582
When the @code{quit} statement is read, the @command{bc} processor
583
is terminated, regardless of where the @code{quit} statement is found. For
584
example, "if (0 == 1) quit" will cause @command{bc} to terminate.
585
586
@item warranty
587
Print a longer warranty notice. This is an extension.
588
@end table
589
590
@node Functions, Examples, Statements, Top
591
@chapter Functions
592
593
@menu
594
* Math Library Functions::
595
@end menu
596
597
Functions provide a method of defining a computation that can be
598
executed later. Functions in @command{bc} always compute a value and
599
return it to the caller. Function definitions are "dynamic" in the
600
sense that a function is undefined until a definition is encountered in
601
the input. That definition is then used until another definition
602
function for the same name is encountered. The new definition then
603
replaces the older definition. A function is defined as follows:
604
605
@example
606
@code{define} @var{name} @code{(} @var{parameters} @code{)} @code{@{} @var{newline}
607
@var{auto_list statement_list} @code{@}}
608
@end example
609
610
A function call is just an expression of the form
611
"@code{name} @code{(}@var{parameters}@code{)}".
612
613
Parameters are numbers or arrays (an extension). In the function definition,
614
zero or more parameters are defined by listing their names separated by
615
commas. Numbers are only call by value parameters. Arrays are only
616
call by variable. Arrays are specified in the parameter definition by
617
the notation "@var{name}@code{[ ]}". In the function call, actual parameters
618
are full expressions for number parameters. The same notation is used
619
for passing arrays as for defining array parameters. The named array is
620
passed by variable to the function. Since function definitions are dynamic,
621
parameter numbers and types are checked when a function is called. Any
622
mismatch in number or types of parameters will cause a runtime error.
623
A runtime error will also occur for the call to an undefined function.
624
625
The @var{auto_list} is an optional list of variables that are for
626
"local" use. The syntax of the auto list (if present) is "@code{auto}
627
@var{name}, ... ;". (The semicolon is optional.) Each @var{name} is
628
the name of an auto variable. Arrays may be specified by using the
629
same notation as used in parameters. These variables have their
630
values pushed onto a stack at the start of the function. The
631
variables are then initialized to zero and used throughout the
632
execution of the function. At function exit, these variables are
633
popped so that the original value (at the time of the function call)
634
of these variables are restored. The parameters are really auto
635
variables that are initialized to a value provided in the function
636
call.
637
Auto variables are different than traditional local variables
638
because if function A calls function B, B may access function
639
A's auto variables by just using the same name, unless function B has
640
called them auto variables. Due to the fact that auto variables and
641
parameters are pushed onto a stack, @command{bc} supports recursive functions.
642
643
The function body is a list of @command{bc} statements. Again, statements
644
are separated by semicolons or newlines. Return statements cause the
645
termination of a function and the return of a value. There are two
646
versions of the return statement. The first form, "@code{return}", returns
647
the value 0 to the calling expression. The second form,
648
"@code{return} ( @var{expression} )", computes the value of the expression
649
and returns that value to the calling expression. There is an implied
650
"@code{return} (0)" at the end of every function. This allows a function
651
to terminate and return 0 without an explicit @code{return} statement.
652
653
Functions also change the usage of the variable @var{ibase}. All
654
constants in the function body will be converted using the value of
655
@var{ibase} at the time of the function call. Changes of @var{ibase}
656
will be ignored during the execution of the function except for the
657
standard function @code{read}, which will always use the current value
658
of @var{ibase} for conversion of numbers.
659
660
As an extension, the format of the definition has been slightly relaxed.
661
The standard requires the opening brace be on the same line as the
662
@code{define} keyword and all other parts must be on following lines.
663
This version of @command{bc} will allow any number of newlines before and
664
after the opening brace of the function. For example, the following
665
definitions are legal.
666
667
@example
668
define d (n) @{ return (2*n); @}
669
define d (n)
670
@{ return (2*n); @}
671
@end example
672
673
674
@node Math Library Functions, , Functions, Functions
675
@section Math Library Functions
676
677
If @command{bc} is invoked with the @code{-l} option, a math library is
678
preloaded and the default @var{scale} is set to 20. The math functions will
679
calculate their results to the scale set at the time of their call. The
680
math library defines the following functions:
681
682
@table @code
683
@item s (@var{x})
684
The sine of @var{x}, @var{x} is in radians.
685
686
@item c (@var{x})
687
The cosine of @var{x}, @var{x} is in radians.
688
689
@item a (@var{x})
690
The arctangent of @var{x}, arctangent returns radians.
691
692
@item l (@var{x})
693
The natural logarithm of @var{x}.
694
695
@item @var{e} (@var{x})
696
The exponential function of raising @var{e} to the value @var{x}.
697
698
@item @var{j} (@var{n,x})
699
The bessel function of integer order @var{n} of @var{x}.
700
@end table
701
702
@node Examples, Readline and Libedit Options, Functions, Top
703
@chapter Examples
704
705
In /bin/sh, the following will assign the value of "pi" to the shell
706
variable @var{pi}.
707
@example
708
709
pi=$(echo "scale=10; 4*a(1)" | bc -l)
710
711
@end example
712
713
The following is the definition of the exponential function used in the
714
math library. This function is written in POSIX @command{bc}.
715
716
@example
717
718
scale = 20
719
720
/* Uses the fact that e^x = (e^(x/2))^2
721
When x is small enough, we use the series:
722
e^x = 1 + x + x^2/2! + x^3/3! + ...
723
*/
724
725
define e(x) @{
726
auto a, d, e, f, i, m, v, z
727
728
/* Check the sign of x. */
729
if (x<0) @{
730
m = 1
731
x = -x
732
@}
733
734
/* Precondition x. */
735
z = scale;
736
scale = 4 + z + .44*x;
737
while (x > 1) @{
738
f += 1;
739
x /= 2;
740
@}
741
742
/* Initialize the variables. */
743
v = 1+x
744
a = x
745
d = 1
746
747
for (i=2; 1; i++) @{
748
e = (a *= x) / (d *= i)
749
if (e == 0) @{
750
if (f>0) while (f--) v = v*v;
751
scale = z
752
if (m) return (1/v);
753
return (v/1);
754
@}
755
v += e
756
@}
757
@}
758
759
@end example
760
761
The following is code that uses the extended features of @command{bc} to
762
implement a simple program for calculating checkbook balances. This
763
program is best kept in a file so that it can be used many times
764
without having to retype it at every use.
765
766
@example
767
768
scale=2
769
print "\nCheck book program\n!"
770
print " Remember, deposits are negative transactions.\n"
771
print " Exit by a 0 transaction.\n\n"
772
773
print "Initial balance? "; bal = read()
774
bal /= 1
775
print "\n"
776
while (1) @{
777
"current balance = "; bal
778
"transaction? "; trans = read()
779
if (trans == 0) break;
780
bal -= trans
781
bal /= 1
782
@}
783
quit
784
785
@end example
786
787
788
The following is the definition of the recursive factorial function.
789
790
@example
791
792
define f (x) @{
793
if (x <= 1) return (1);
794
return (f(x-1) * x);
795
@}
796
797
@end example
798
799
@node Readline and Libedit Options, GNU @command{bc} and Other Implementations, Examples, Top
800
@chapter Readline and Libedit Options
801
802
GNU @command{bc} can be compiled (via a configure option) to use the GNU
803
@command{readline} input editor library or the BSD @command{libedit}
804
library. This allows the user to do
805
more editing of lines before sending them to @command{bc}. It also
806
allows for a history of previous lines typed. When this option is
807
selected, @command{bc} has one more special variable. This special
808
variable, @var{history} is the number of lines of history retained. A
809
value of -1 means that an unlimited number of history lines are
810
retained. This is the default value. Setting the value of
811
@var{history} to a positive number restricts the number of history lines
812
to the number given. The value of 0 disables the history feature. For
813
more information, read the user manuals for the GNU @command{readline},
814
@command{history} and BSD @command{libedit} libraries. One can not
815
enable both @command{readline} and @command{libedit} at the same time.
816
817
@node GNU @command{bc} and Other Implementations, Limits, Readline and Libedit Options, Top
818
@chapter GNU @command{bc} and Other Implementations
819
820
This version of @command{bc} was implemented from the POSIX P1003.2/D11
821
draft and contains several differences and extensions relative to the
822
draft and traditional implementations. It is not implemented in the
823
traditional way using @command{dc}. This version is a single process
824
which parses and runs a byte code translation of the program. There is
825
an "undocumented" option (-c) that causes the program to output the byte
826
code to the standard output instead of running it. It was mainly used
827
for debugging the parser and preparing the math library.
828
829
A major source of differences is extensions, where a feature is extended
830
to add more functionality and additions, where new features are added.
831
The following is the list of differences and extensions.
832
833
@table @var
834
835
@item LANG environment
836
This version does not conform to the POSIX standard in the processing
837
of the LANG environment variable and all environment variables starting
838
with LC_.
839
840
@item names
841
Traditional and POSIX @command{bc}
842
have single letter names for functions, variables and arrays. They have
843
been extended to be multi-character names that start with a letter and
844
may contain letters, numbers and the underscore character.
845
846
@item Strings
847
Strings are not allowed to contain NUL characters. POSIX says all characters
848
must be included in strings.
849
850
@item last
851
POSIX @command{bc} does not have a \fBlast variable. Some implementations
852
of @command{bc} use the period (.) in a similar way.
853
854
@item comparisons
855
POSIX @command{bc} allows comparisons only in the @code{if} statement,
856
the @code{while} statement, and the second expression of the @code{for}
857
statement. Also, only one relational operation is allowed in each of
858
those statements.
859
860
@item if statement, else clause
861
POSIX @command{bc} does not have an @code{else} clause.
862
863
@item for statement
864
POSIX @command{bc} requires all expressions to be present in the
865
@code{for} statement.
866
867
@item &&, ||, !
868
POSIX @command{bc} does not have the logical operators.
869
870
@item read function
871
POSIX @command{bc} does not have a @code{read} function.
872
873
@item print statement
874
POSIX @command{bc} does not have a @code{print} statement.
875
876
@item continue statement
877
POSIX @command{bc} does not have a continue statement.
878
879
@item array parameters
880
POSIX @command{bc} does not (currently) support array parameters in full.
881
The POSIX grammar allows for arrays in function definitions, but does
882
not provide a method to specify an array as an actual parameter. (This
883
is most likely an oversight in the grammar.) Traditional implementations
884
of @command{bc} have only call by value array parameters.
885
886
@item function format
887
POSIX @command{bc} requires the opening brace on the same line as the
888
@code{define} key word and the @code{auto} statement on the next line.
889
890
@item =+, =-, =*, =/, =%, =^
891
POSIX @command{bc} does not require these "old style" assignment
892
operators to be defined. This version may allow these "old style"
893
assignments. Use the @code{limits} statement to see if the installed
894
version supports them. If it does support the "old style" assignment
895
operators, the statement "a =- 1" will decrement @code{a} by 1 instead
896
of setting @code{a} to the value -1.
897
898
@item spaces in numbers
899
Other implementations of @command{bc} allow spaces in numbers. For example,
900
"x=1 3" would assign the value 13 to the variable x. The same statement
901
would cause a syntax error in this version of @command{bc}.
902
903
@item errors and execution
904
This implementation varies from other implementations in terms of what
905
code will be executed when syntax and other errors are found in the
906
program. If a syntax error is found in a function definition, error
907
recovery tries to find the beginning of a statement and continue to
908
parse the function. Once a syntax error is found in the function, the
909
function will not be callable and becomes undefined.
910
Syntax errors in the interactive execution code will invalidate the
911
current execution block. The execution block is terminated by an
912
end of line that appears after a complete sequence of statements.
913
For example,
914
915
@example
916
a = 1
917
b = 2
918
@end example
919
920
has two execution blocks and
921
922
@example
923
@{ a = 1
924
b = 2 @}
925
@end example
926
927
has one execution block. Any runtime error will terminate the execution
928
of the current execution block. A runtime warning will not terminate the
929
current execution block.
930
931
@item Interrupts
932
During an interactive session, the SIGINT signal (usually generated by
933
the control-C character from the terminal) will cause execution of the
934
current execution block to be interrupted. It will display a "runtime"
935
error indicating which function was interrupted. After all runtime
936
structures have been cleaned up, a message will be printed to notify the
937
user that @command{bc} is ready for more input. All previously defined
938
functions remain defined and the value of all non-auto variables are the
939
value at the point of interruption. All auto variables and function
940
parameters are removed during the clean up process. During a
941
non-interactive session, the SIGINT signal will terminate the entire run
942
of @command{bc}.
943
@end table
944
945
@node Limits, Environment Variables, GNU @command{bc} and Other Implementations, Top
946
@chapter Limits
947
948
The following are the limits currently in place for this @command{bc}
949
processor. Some of them may have been changed by an installation. Use
950
the @code{limits} statement to see the actual values.
951
952
@table @code
953
954
@item BC_BASE_MAX
955
The maximum output base is currently set at 999. The maximum input base
956
is 16.
957
958
@item BC_DIM_MAX
959
This is currently an arbitrary limit of 65535 as distributed. Your
960
installation may be different.
961
962
@item BC_SCALE_MAX
963
The number of digits after the decimal point is limited to INT_MAX digits.
964
Also, the number of digits before the decimal point is limited to INT_MAX
965
digits.
966
967
@item BC_STRING_MAX
968
The limit on the number of characters in a string is INT_MAX characters.
969
970
@item exponent
971
The value of the exponent in the raise operation (^) is limited to LONG_MAX.
972
973
@item multiply
974
The multiply routine may yield incorrect results if a number
975
has more than LONG_MAX / 90 total digits. For 32 bit longs, this number is
976
23,860,929 digits.
977
978
@item variable names
979
The current limit on the number of unique names is 32767 for each of
980
simple variables, arrays and functions.
981
@end table
982
983
@node Environment Variables, , Limits, Top
984
@chapter Environment Variables
985
986
The following environment variables are processed by @command{bc}:
987
988
@table @code
989
990
991
@item POSIXLY_CORRECT
992
This is the same as the -s option (@pxref{Command Line Options}).
993
994
@item BC_ENV_ARGS
995
This is another mechanism to get arguments to @command{bc}. The format
996
is the same as the command line arguments. These arguments are
997
processed first, so any files listed in the environent arguments are
998
processed before any command line argument files. This allows the user
999
to set up "standard" options and files to be processed at every
1000
invocation of @command{bc}. The files in the environment variables
1001
would typically contain function definitions for functions the user
1002
wants defined every time @command{bc} is run.
1003
1004
@item BC_LINE_LENGTH
1005
This should be an integer specifing the number of characters in an
1006
output line for numbers. This includes the backslash and newline
1007
characters for long numbers.
1008
@end table
1009
1010
@contents
1011
@bye
1012
1013
Loggerhead is a web-based interface for Breezy
Version: 2.0.1