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Plan 9 - man page for bc (plan9 section 1)

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BC(1)											    BC(1)

       bc - arbitrary-precision arithmetic language

       bc [ -c ] [ -l ] [ file ...  ]

       Bc  is an interactive processor for a language that resembles C but provides arithmetic on
       numbers of arbitrary length with up to 100 digits right of the decimal  point.	It  takes
       input from any files given, then reads the standard input.  The -l argument stands for the
       name of an arbitrary precision math library.  The following syntax for bc programs is like
       that of C; L means letter a-z, E means expression, S means statement.


	      comments are enclosed in /* */

	      newlines end statements


	      simple variables: L
	      array elements: L[E]
	      The words ibase, obase, and scale

       Other operands

	      arbitrarily long numbers with optional sign and decimal point.



		     number of significant decimal digits

		     number of digits right of decimal point

		     function call


	      +  -  *  /  %  ^	(% is remainder; ^ is power)

	      ++  --

	      ==  <=  >=  !=  <  >

	      =  +=  -=  *=  /=  %=  ^=

	      { S ; ...  ; S }
	      print E
	      if ( E ) S
	      while ( E ) S
	      for ( E ; E ; E ) S
	      null statement

       Function definitions
	      define L ( L , ...  , L ){
	      auto L , ...  , L
	      S ; ...  ; S
	      return E


       Functions in
	      -l math library

	      s(x)   sine

	      c(x)   cosine

	      e(x)   exponential

	      l(x)   log

	      a(x)   arctangent

	      j(n, x)
		     Bessel function

       All function arguments are passed by value.

       The  value  of  an  expression  at the top level is printed unless the main operator is an
       assignment.  Text in quotes, which may include newlines, is also  printed.   Either  semi-
       colons  or newlines may separate statements.  Assignment to scale influences the number of
       digits to be retained on arithmetic operations in the manner  of  dc(1).   Assignments  to
       ibase or obase set the input and output number radix respectively.

       The same letter may be used as an array, a function, and a simple variable simultaneously.
       All variables are global to the program.  Automatic variables are pushed down during func-
       tion  calls.   In  a  declaration of an array as a function argument or automatic variable
       empty square brackets must follow the array name.

       Bc is actually a preprocessor for dc(1), which it invokes  automatically,  unless  the  -c
       (compile  only) option is present.  In this case the dc input is sent to the standard out-
       put instead.

       Define a function to compute an approximate value of the exponential.  Use it to print  10
       values.	(The exponential function in the library gives better answers.)

       scale = 20
       define e(x) {
	    auto a, b, c, i, s
	    a = 1
	    b = 1
	    s = 1
	    for(i=1; 1; i++) {
		 a *= x
		 b *= i
		 c = a/b
		 if(c == 0) return s
		 s += c
       for(i=1; i<=10; i++) print e(i)

       /sys/lib/bclib mathematical library


       dc(1), hoc(1)

       No or operators.
       A statement must have all three
       A is interpreted when read, not when executed.

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