Click here to download gcdfun2.c.

/******************************************
 This Program gets two positive integers
 from the user and computes their GCD.
 ******************************************/
#include <stdio.h>

int getposint();
int gcd(int a, int b);

int main() {
  int a = getposint();
  int b = getposint();

  // Compute the gcd
  int g = gcd(a, b);

  // Write out gcd
  printf("The gcd is %i\n", g);

  return 0;
}

/******************************************
 This function gets a positive integer
 from the user
 ******************************************/
int getposint() {
  int k;

  printf("Enter a positive integer: ");
  fflush(stdout);
  int check = scanf(" %i", &k);

  while(check < 1 || k <= 0) {
    printf("I said *positive*, try again: ");
    fflush(stdout);
    check = scanf(" %i", &k);
  }

  return k;
}

/******************************************
 This function computes the gcd of two
 integers.
 ******************************************/
int gcd(int a, int b) {
  while(b != 0) {
    int r = a % b;
    a = b;
    b = r;
  }
  return a;
}