rexx/progs/fact.r

   1 /* recursion test of factorial */
   2 /* note: this implementation of rexx uses two kinds of
   3          of numbers integers (C long (4-bytes) numbers from -2E9 upto 2E9),
   4          and real (C double precision numbers). It's better
   5          to use a real number ie 45.0 instead of 45 for large
   6          factorials since the later will result to a factorial using
   7          integer arithmetic resulting in a crazy result
   8          (15 is the largest integer factorial that can be calculated
   9           with out any error )
  10 */
  11 if arg() ^= 1 then do
  12         say 'Enter a number'
  13         pull num
  14 end; else do
  15         num = arg(1)
  16 end
  17
  18 if datatype(num) ^= 'NUM' | num < 0 then do
  19         say 'Invalid number "'num'"'
  20         exit 2
  21 end
  22
  23 /* you can even translate the number to real with the following instr */
  24 /* num = num + 0.0 /* so from now on num will be treated as real */ */
  25
  26 say num'! = 'fact(num)
  27 exit
  28
  29 fact: procedure
  30 if arg(1)<=0 then return 1
  31 return  fact(arg(1)-1)*arg(1)