GCD logical error

I wrote this code to get the gcd in c. It works perfectly for small numbers but when I tried 60 and 90 for example I got 2, while getting 3 for 9 &6.

#include "stdio.h"
#include "stdlib.h"
int main()
{
    int a,b,x,gcd;
    printf("Please Enter the fraction");
    scanf("%d", &a);
    scanf("%d", &b);
    if(b%a == 0)
        gcd =a;
    else
    {
        x=a;
        while(--x>1)
        {
            if (a%x == 0 && b%x==0)
            {  
                 gcd =x;
            }
        }
    }
    printf("GCD = %d", gcd);
    return 0;
}