MENU driven program ( 1-factorial, 2-Isprime,3-GCD,4-exit)

#include <stdio.h>
#include<stdio.h>
int factorial(int a);
int main()
{
    int f,a,num,b,n1,n2,gcd;
    printf("enter a number between 1 and 4: ");
    scanf("%d", &num);
    printf("Enter a number:\n");
    switch(num)
    {
    case 1:
        scanf("%d", &a);
        f= factorial(a);
        printf("Factorial = %d", f);
        break;

    case 2:
        scanf("%d", &b);
        int count=0,z=0;
        for(int i=2; i<b; i++)
        {
            if(b%i==0)
            {
                count++;
                break;
            }

        }
        if (count==0)
            printf("prime number");
        else
            printf("not a prime");
        break;


    case 3:

        printf("Enter two integers:");
        scanf("%d %d", &n1, &n2);

        for(int i=1; i <= n1 && i <= n2; i++)
        {
            if(n1%i==0 && n2%i==0)
                gcd = i;
        }
        printf("GCD = %d", gcd);
        break;

    case 4:
        printf("exit");

    }


    return 0;


}
int factorial(int a)
{
    int fact=1;
    for(int i=1; i<=a; i++)
    {
        fact*=i;
    }
    return fact;
}