Hello All!

I am trying to learn Rexx.  I am studying Rexx in 21 days by William &
Esther Schindler.  I got to this example of recursion & cannot figure
it out.

This program figures the factorial of a number. Would someone please
explain how this works.


[C:\rexx_in_21]list1406
     5 *-*   Say 'Enter a number:';
       >>>     "Enter a number:"
Enter a number:
     6 *-*   Pull number;
5
       >>>     "5"
     7 *-*   Say number || '! is' Factorial(number);
    10 *-*     Factorial:
    10 *-*     Procedure;
    11 *-*     num = Arg(1);
       >>>       "5"
    12 *-*     If num = 1;
       >>>       "0"
    14 *-*     Return Factorial(num - 1) * num;       /* I thought this
should be (5-1) X 5 or 20 */
    10 *-*       Factorial:
    10 *-*       Procedure;
    11 *-*       num = Arg(1);
       >>>         "4"
    12 *-*       If num = 1;
       >>>         "0"
    14 *-*       Return Factorial(num - 1) * num;
    10 *-*         Factorial:
    10 *-*         Procedure;
    11 *-*         num = Arg(1);
       >>>           "3"
    12 *-*         If num = 1;
       >>>           "0"
    14 *-*         Return Factorial(num - 1) * num;
    10 *-*           Factorial:
    10 *-*           Procedure;
    11 *-*           num = Arg(1);
       >>>             "2"
    12 *-*           If num = 1;
       >>>             "0"
    14 *-*           Return Factorial(num - 1) * num;
    10 *-*             Factorial:
    10 *-*             Procedure;
    11 *-*             num = Arg(1);
       >>>               "1"
    12 *-*             If num = 1;
       >>>               "1"
    12 *-*             Then;
    13 *-*               Return num;
       >>>                 "1"                          
  /* where did this come from */
       >>>             "2"                              
  /*      "        "      "      "           "   
*/
       >>>           "6"                                
  /*      "        "      "      "           "   
*/
       >>>         "24"                                 
 /*      "        "      "      "           "   
*/
       >>>       "120"                                  
/*      "        "      "      "           "    */
       >>>     "5! is 120"
5! is 120
     8 *-*   Exit;

Thanks for the help,

Steven

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