expo.c

   1 /*
   2  * Exponentiation using recursion
   3  *
   4  * Luiz Fernando N. Capitulino
   5  * <lcapitulino@gmail.com>
   6  */
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9
  10 double expr(int base, int n)
  11 {
  12         if (!n)
  13                 return 1;
  14         return (base * expr(base, n - 1));
  15 }
  16
  17 int main(int argc, char *argv[])
  18 {
  19         int base, expo;
  20
  21         if (argc != 3) {
  22                 printf("expo < base > < exponent>\n");
  23                 exit(1);
  24         }
  25
  26         base = atoi(argv[1]);
  27         expo = atoi(argv[2]);
  28
  29         if (expo < 0) {
  30                 fprintf(stderr, "error: the exponent must be positive\n");
  31                 exit(1);
  32         }
  33
  34         printf("%d exp %d = %.1f\n", base, expo, expr(base, expo));
  35         return 0;
  36 }