The following code shows how to Find the Greatest Common Divisor (GCD) of Two Numbers in C.

// Find Greatest Common Divisor of Two Numbers

#include <stdio.h>

int main()
{
    int first, second, i, gcd, last;
    printf("Enter First Number: ");
    scanf("%d", &first);
    printf("Enter second Number: ");
    scanf("%d", &second);

    if(first<second)
        last=second/2;
    else
        last=first/2;
    for(i=last;i>=1;i--)
    {
        if((first%i==0) && (second%i==0))
        {
            gcd=i;
            break;
        }
    }
    printf("GCD of %d and %d is %d", first, second, gcd);
    
    return 0;
}

Output

Enter First Number: 945
Enter second Number: 30
GCD of 945 and 30 is 15

Further Reading

50+ C Programming Interview Questions and Answers

C Program to Find Factorial of a Number