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===== GNU bc Cheat Sheet =====

==== Overview ====

*  [[http://en.wikipedia.org/wiki/Bc_programming_language | bc ]] is a command-line calculator and primitive language

*  bc is a [[http://www.opengroup.org/onlinepubs/009695399/utilities/bc.html |POSIX standard]] but the [[http://www.gnu.org/software/bc/ | GNU version]] has added functionality

*  bc by default runs in integer mode (scale=0) and with no trig functions, running ''bc -l'' loads trig functions and sets scale to 20

*  bc can only take expressions on standard input or in files, not directly on the command line. One way to do a bc one-liner is ''echo 3+4 | bc'' .

* [[http://www.phodd.net/cyrek/gnu-bc/ | This]] is a great collection of bc functions. funcs.bc and logic.bc  are the basic ones. [[ http://x-bc.sourceforge.net/extensions_bc.html | This]] is a collection of more sanely named basic scientific calculator functions.

*  useful bash aliases
<code bash>
mbc ()
{
  echo $@ | bc -l -q ~/bin/extensions.bc
}

alias bc="bc -l -q ~/bin/extensions.bc"
</code>
 
So now '' mbc '(3+5)/6' '' works as expected

* bc uses readline so ⇑ and ⇓ (for history) and ctrl-r (for searching) work as expected.

==== Basic Usage ====

* Any alphanumeric variable name is allowed once it starts with a letter.

* There are 4 special variables
    * ''last'' - The value of the last printed number
    * ''scale'' - number of decimal places to display
    * ''ibase'' - base to be used for input values
    * ''obase'' - base to be used for output values

*  Any expression that is not an assignment is displayed and stored in the ''last'' variable.

* Every value and every expression is a number. The assignment operator returns 0. Booleans are 0 / 1.

* Basic + - / * = == work. % is modulo . ^ is integer exponentiation.

* Predefined functions are :
    * s - sine , c - cosine
    * a - arctan , j(n,x) - Bessel function
    * l - natural log , e - e to the power of
    * length, scale, sqrt - as named

* && , || , ! work as expected (return 0 or 1).

==== Advanced Usage ====

* New functions are easy to define e.g. <code>
define log(x,y) {
  auto retval = l(y)/l(x)
  return retval
}</code>
Note that the ''auto'' keyword is used to declare a local variable.

* ''if(cond) else'', ''while(cond)'' and ''for(init;cond;inc)'' control flow structures are all supported. ''break'' and ''continue'' are also supported.

* ''read()'' is used to read a value from standard input. ''print()'' prints to standard output.

* Arrays can be used by using ''[subscript]'' after the array name.

* Special commands include ''quit'', ''limits'' and ''warranty''.

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