Euclidean algorithm for GCD

#include <stdio.h>
void swap(int *a, int *b){
    int temp = *a;
    *a = *b;
    *b = temp;
}
int gcd(int a, int b){
    if(a < b) swap(&a, &b);
    int r = a % b;
    printf("\n%d\t=\t%d\t*\t%d\t+\t%d", a, a/b, b, r);
    if (r == 0) return b;
    gcd (b, r);
}
int main(){
    printf("Enter two numbers to find out their GCD:-\n");
    int a, b;
    scanf("%d", &a);
    scanf("%d", &b);
    printf("\n\nSo, %d is the GCD of %d and %d\n", gcd(a, b), a, b);
}