Bc (programming language): Difference between revisions

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{{Short description|Arbitrary-precision calculator supporting interactive and scripted use}}{{Not to be confused with|B programming language|C programming language}}{{more footnotes|date=June 2013}}

{{more footnotes|date=June 2013}}

{{lowercase|title=bc programming language}}

{{Infobox software

'''bc''', for ''basic calculator'' (often referred to as ''bench calculator''), is "''an [[Arbitrary-precision arithmetic|arbitrary-precision]] calculator language''" with syntax similar to the [[C (programming language)|C programming language]]. bc is typically used as either a mathematical scripting language or as an interactive mathematical shell.

| name = bc

| logo =

| screenshot =

| screenshot size =

| caption =

| developer = [[Robert Morris (cryptographer)|Robert Morris]] and [[Lorinda Cherry]] of [[Bell Labs]]

| released = {{Release year|df=yes|1975}}

| latest release version =

| latest release date =

| operating system = [[Unix]], [[Unix-like]], [[Plan 9 from Bell Labs|Plan 9]], [[FreeDOS]]

| platform = [[Cross-platform]]

| genre = [[Command (computing)|Command]]

| license =

| website =

}}

'''bc''', for ''basic calculator'', is an [[Arbitrary-precision arithmetic|arbitrary-precision]] [[math]]ematical [[calculator]] [[computer program|program]] with an input language similar to [[C (programming language)|C]]. It supports both interactive, [[command-line interface|command-line]] [[user-interface]] and script processing.

==Overview==

A typical interactive usage is typing the command <code>bc</code> on a [[Unix]] [[Command-line interface#Command prompt|command prompt]] and entering a mathematical expression, such as {{code|(1 + 3) * 2}}, whereupon {{samp|8}} will be output. While bc can work with arbitrary precision, it actually defaults to zero digits after the decimal point, so the expression {{code|2/3}} yields {{samp|0}} (results are truncated, not rounded). This can surprise new bc users unaware of this fact. The {{code|-l}} option to bc sets the default ''scale'' (digits after the decimal point) to 20 and adds several additional mathematical functions to the language.

==History==

bc first appeared in [[Version 6 Unix]] in 1975. andIt was written by [[Robert Morris (cryptographer)|Robert Morris]] and [[Lorinda Cherry]] of [[Bell Labs]]. bcas wasa precededfront byend to [[dc (computer program)|dc]], an earlier arbitrary-precision calculator written by the[[Robert sameMorris (cryptographer)|Robert authorsMorris]] and Cherry. dc could doperformed arbitrary-precision calculations,computations butspecified itsin [[reverse Polish notation]] (RPN) syntax was inconvenient for users, and therefore. bc wasprovided writtena asconventional a frontprogramming-endlanguage interface to dc.the bcsame wascapability avia verya simple [[compiler]] (a single [[yacc]] source file withcomprising a few hundred lines of code), which converted thea new,[[C (programming language)|C]]-like, bc syntax into dc's [[postfix notation]] and [[Pipeline (Unix)|piped]] the results through dc.

In 1991, [[POSIX]] rigorously defined and standardized bc. TwoFour implementations of this standard survive today: The first is the traditional Unix implementation, a front-end to dc, which survives in Unix and [[Plan 9 from Bell Labs|Plan 9]] systems. The second is the [[free software]] [[GNU]] bc, first released in 1991 by Philip A. Nelson. The GNU implementation has numerous extensions beyond the POSIX standard and is no longer a front-end to dc (it is a [[bytecode interpreter]]). The third is a re-implementation by [[OpenBSD]] in 2003. The fourth is an independent implementation by Gavin Howard<ref name=":1">[https://git.gavinhoward.com/gavin/bc An implementation of Unix dc and POSIX bc with GNU and BSD extensions]</ref> that is included in [[Android (operating system)]],<ref name=":2">{{Cite web|url=https://android.googlesource.com/platform/system/core/+/master/shell_and_utilities/README.md|title=Android's shell and utilities|website=android.googlesource.com}}</ref><ref name=":3">{{cite web | url=https://android.googlesource.com/platform/external/bc/ | title=Platform/External/Bc - Git at Google }}</ref> [[FreeBSD]] as of 13.3-RELEASE,<ref name=":4">{{Cite web|url=https://forums.freebsd.org/threads/freebsd-13-3-whats-new-and-how-did-we-get-here.92596/|title=FreeBSD 13.3: What's new, and how did we get here?|date=March 5, 2024|website=The FreeBSD Forums}}</ref><ref name=":5">{{Cite web|url=https://man.freebsd.org/cgi/man.cgi?query=bc&apropos=0&sektion=1&manpath=FreeBSD+14.1-RELEASE&arch=default&format=html|title=bc(1)|website=man.freebsd.org}}</ref><ref name=":6">{{Cite web|url=https://cgit.freebsd.org/src/tree/contrib/bc|title=bc « contrib - src - FreeBSD source tree|website=cgit.freebsd.org}}</ref> and [[macOS]] as of 13.0.<ref name=":7">{{Cite web|url=https://opensource.apple.com/releases/|title=Apple Open Source|website=opensource.apple.com}}</ref><ref name=":8">{{Cite web|url=https://github.com/apple-oss-distributions/bc/tree/main/bc|title=bc/bc at main · apple-oss-distributions/bc|website=GitHub}}</ref><ref name=":9">{{cite web | url=https://gavinhoward.com/2023/02/my-code-conquered-another-os/ | title=My Code Conquered Another OS! &#124; Gavin D. Howard }}</ref>

== POSIX bc Implementations==

===POSIX bc===

The POSIX standardized bc language is traditionally written as a program in the [[dc (computer program)|dc]] programming language to provide a higher level of access to the features of the dc language without the complexities of dc's terse syntax.

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All numbers and variable contents are [[arbitrary-precision]] numbers whose precision (in decimal places) is determined by the global '''<code>scale</code>''' variable.

The [[base (exponentiation)radix|numeric base]] of input (in interactive mode), output and program constants may be specified by setting the reserved '''<code>ibase</code>''' (input base) and '''<code>obase</code>''' (output base) variables.

Output is generated by deliberately not assigning the result of a calculation to a variable.

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Comments may be added to bc code by use of the C '''<code>/*</code>''' and '''<code>*/</code>''' (start and end comment) symbols.

=== =Mathematical operators ====

==== Exactly as C ====

==== =Exactly as C =====

The following POSIX bc [[Operator (programming)|operators]] behave exactly like their C counterparts:

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( ) [ ] { }

==== =Similar to C =====

The [[Modulus operator|modulus]] operators, <code>%</code> and <code>%=</code> behave exactly like their C counterparts only when the global '''<code>scale</code>''' variable is set to 0, i.e. all calculations are integer-only. Otherwise the computation is done with the appropriate scale. <code>a%b</code> is defined as <code>a-(a/b)*b</code>. Examples:

<sourcesyntaxhighlight lang="console" highlight="6,8,10">

$ bc

bc 1.06

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scale=20; 5%3

.00000000000000000002

</syntaxhighlight>

</source>

==== =Conflicting with C =====

The operators

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Of particular note, the use of the <code>^</code> operator with negative numbers does not follow the C operator precedence. <code>-2^2</code> gives the answer of 4 under bc rather than −4.

==== ="Missing" operators relative to C =====

The [[bitwise operation|bitwise]], [[Boolean logic|booleanBoolean]] and [[conditional (programming)|conditional]] operators:

& | ^ && ||

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are not available in POSIX bc.

=== =Built-in functions ====

The '''<code>sqrt()</code>''' function for calculating [[square root]]s is POSIX bc's only built-in mathematical function. Other functions are available in an external standard library.

The '''<code>scale()</code>''' function for determining the precision (as with the '''<code>scale</code>''' variable) of its argument and the '''<code>length()</code>''' function for determining the number of significant decimal digits in its argument are also built-in.

=== =Standard library functions ====

bc's standard math library (defined with the '''-l''' option) contains functions for calculating [[sine]], [[cosine]], [[arctangent]], [[natural logarithm]], the [[exponential function]] and the two parameter [[Bessel function]] ''J''. Most standard mathematical functions (including the other inverse trigonometric functions) can be constructed using these. See external links for implementations of many other functions.

{| class="wikitable"

|+The bc standard library<ref name=":0">{{Cite webman|url=https://www.gnu.org/software/bc/manual/html_mono/bc.html#SEC18cu|title=bc Command Manual|last=NelsonSUS|first=Philiparbitrary-precision A.|date=20arithmetic March 2001|website=|publisher=[[Free Software Foundation]]|access-date=2017-04-20language}}</ref>

!bc command

!Function

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The '''-l''' option changes the scale to 20,<ref name=":0" /> so things such as modulo may work unexpectedly. For example, writing <code>bc -l</code> and then the command <code>print 3%2</code> outputs 0. But writing <code>scale=0</code> after <code>bc -l</code> and then the command <code>print 3%2</code> will output 1.

== =Plan 9 bc ===

[[Plan 9 from Bell Labs|Plan 9]] bc is identical to POSIX bc but for an additional '''<code>print</code>''' statement.

== =GNU bc ===

GNU bc derives from the POSIX standard and includes many enhancementsextensions. It is entirely separate from dc-based implementations of the POSIX standard and is instead written in C. Nevertheless, it is fully backwards compatible as all POSIX bc programs will run unmodified as GNU bc programs.

GNU bc variables, arrays and function names may contain more than one character, some more operators have been included from C, and notably, an '''<code>if</code>''' clause may be followed by an '''<code>else</code>'''.

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The value of the last calculation is always stored within the additional built-in '''<code>last</code>''' variable.

=== =Extra operators ====

The following [[logical operator]]s are additional to those in POSIX bc:

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They are available for use in conditional statements (such as within an '''<code>if</code>''' statement). Note, however, that there are still no equivalent bitwise or assignment operations.

=== =Functions ====

All functions available in GNU bc are inherited from POSIX. No further functions are provided as standard with the GNU distribution.

== Example code ==

Since the bc <code>^</code> operator only allows an integer power to its right, one of the first functions a bc user might write is a power function with a floating-point exponent. Both of the below assume the standard library has been included:

=== A "power" function in POSIX bc ===

<syntaxhighlight lang="bc">

/* A function to return the integer part of x */

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</syntaxhighlight>

=== Calculating π to 10000 places digits===

=== An equivalent "power" function in GNU bc ===

<syntaxhighlight lang="c">

# A function to return the integer part of a number

define int(number) {

auto oldscale

oldscale = scale

scale = 0

number /= 1 /* round number down */

scale = oldscale

return number

}

# Use the fact that number^exponent == e^(exponent*log(number))

define power(number,exponent) {

if (exponent == int(exponent)) {

return number ^ int(exponent)

} else {

return e( exponent * l(number) )

}

}

</syntaxhighlight>

=== Calculating π to 10000 places ===

Calculate [[pi]] using the builtin [[Inverse trigonometric functions|arctangent]] function, {{mono|a()}}:

<syntaxhighlight lang="console" highlight="3">

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</syntaxhighlight>

=== A translated C function ===

Because the syntax of bc is similar to that of [[C (programming language)|C]], published numerical functions written in C can often be translated into bc quite easily, which immediately provides the arbitrary precision of bc. For example, in the [[Journal of Statistical Software]] (July 2004, Volume 11, Issue 5), [[George Marsaglia]] published the following C code for the [[normal distribution|cumulative normal distribution]]:

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</syntaxhighlight>

With some necessary changes to accommodate bc's different syntax, and realizingnoting that the constant "0.9189..." is actually log(2*PI)/2, this can be translated to the following GNU bc code:

<syntaxhighlight lang="bc">

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</syntaxhighlight>

== Using bc in shell scripts ==

bc can be used non-interactively, with input through a [[Pipeline (Unix)|pipe]]. This is useful inside [[shell script]]s. For example:

<sourcesyntaxhighlight lang="console">

$ result=$(echo "scale=2; 5 * 7 /3;" | bc)

$ echo $result

11.66

</syntaxhighlight lang="c">

</source>

In contrast, note that the [[Bash (Unix shell)|bash shell]] only performs integer arithmetic, e.g.:

<sourcesyntaxhighlight lang="console">

$ result=$((5 * 7 /3))

$ echo $result

11

</syntaxhighlight>

</source>

One can also use the [[Here document|here-string]] idiom (in bash, ksh, csh):

<sourcesyntaxhighlight lang="console">

$ bc -l <<< "5*7/3"

11.66666666666666666666

</syntaxhighlight>

</source>

== See also ==

* [[dc (computer program)|dc programming language]]

* [[C (programming language)|C programming language]]

* [[hoc (programming language)|hoc programming language]]

== References ==

{{Reflist}}

{{Refbegin}}

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* [https://www.gnu.org/software/bc/manual/html_mono/bc.html GNU bc manual page]

* [https://web.archive.org/web/20090501204511/http://manpages.ubuntu.com/manpages/jaunty/en/man1/bc.1posix.html POSIX bc manual page]

* {{man|1|bc|Plan 9}}

* [http://plan9.bell-labs.com/magic/man2html/1/bc Plan 9 bc manual page]

* [http://plan9.bell-labs.com/7thEdMan/vol2/bc 7th Edition Unix bc manual page] {{Webarchive|url=https://web.archive.org/web/20061008193920/http://plan9.bell-labs.com/7thEdMan/vol2/bc |date=2006-10-08 }}

* [http://compilers.iecc.com/comparch/article/95-09-015 A comp.compilers article on the design and implementation of C-bc]

* [http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/source/s1/bc.y 6th Edition Unix bc source code], the first release of bc, from May 1975, compiling bc syntax into dc syntax

* [http://ftp.gnu.org/gnu/bc/ GNU bc source code]

{{Refend}}

== External links ==

{{Wikibooks|Guide to Unix|Commands}}

* [https://doi.acm.org/10.1145/152923.152925 Dittmer, I. 1993. Error in Unix commands dc and bc for multiple-precision-arithmetic. SIGNUM Newsl. 28, 2 (Apr. 1993), 8&ndash;11.]

* [http://www.phodd.net/cyrek/gnu-bc/ Collection of useful GNU bc functions]

* [https://www.gnu.org/software/bc/ GNU bc] (and an [http://alpha.gnu.org/gnu/bc/ alpha version]) from the Free Software Foundation

* [https://web.archive.org/web/20160222234922/http://gnuwin32.sourceforge.net/packages/bc.htm bc for Windows] from [[GnuWin32]]

* [https://github.com/gavinhoward/bc Gavin Howard bc] - another open source implementation of bc by Gavin Howard with GNU and BSD extensions

* [https://web.archive.org/web/20160304084708/http://x-bc.sourceforge.net/ X-bc] - A Graphical User Interface to bc

** [http://x-bc.sourceforge.net/extensions_bc.html extensions.bc] - contains functions of trigonometry, exponential functions, functions of number theory and some mathematical constants

** [https://web.archive.org/web/20160304092132/http://x-bc.sourceforge.net/scientific_constants_bcextensions_bc.html scientific_constantsextensions.bc] - contains particlefunctions massesof trigonometry, basicexponential constantsfunctions, such as speedfunctions of lightnumber in the vacuumtheory and thesome gravitationalmathematical constantconstants

** [https://web.archive.org/web/20160304081309/http://x-bc.sourceforge.net/scientific_constants_bc.html scientific_constants.bc] - contains particle masses, basic constants, such as speed of light in the vacuum and the gravitational constant

{{unixUnix commands}}

{{Plan 9 commands}}

[[Category:Software calculators]]

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[[Category:Standard Unix programs]]

[[Category:Unix SUS2008 utilities]]

[[Category:Plan 9 commands]]