Figure 10.14  Program Using Recursive Function gcd
/*
 *  Displays the greatest common divisor of two integers
 */

#include <stdio.h>

/*
 *  Finds the greatest common divisor of m and n
 *  Pre:  m and n are both > 0
 */
int
gcd(int m, int n)
{
      int ans;

      if (m % n == 0)
            ans = n;
      else
            ans = gcd(n, m % n);

      return (ans);
}
 
int
main(void)
{
      int n1, n2;

      printf("Enter two positive integers separated by a space> ");
      scanf("%d%d", &n1, &n2);
      printf("Their greatest common divisor is %d\n", gcd(n1, n2));

      return (0);
}

Enter two positive integers separated by a space> 24 84
Their greatest common divisor is 12