Program:

#include<stdio.h>
int main()
{
    int num1, num2,rem=0,lcm,gcd, n1,n2;
    printf("Enter Two  Numbers:");
    scanf("%d%d",&num1,&num2);
    n1=num1;
    n2=num2;
    rem=num1%num2;
    while(rem != 0)
    {
        num1=num2;
        num2=rem;
        rem=num1%num2;
    }
    gcd=num2;
    lcm=(n1*n2)/gcd;
    printf("\n\t-->> GCD of %d and %d is %d", n1,n2,gcd);
    printf("\n\t-->> LCM of %d and %d is %d\n",n1,n2,lcm);
}

Expected O/P:

Enter Two  Numbers:12
9

-->> GCD of 12 and 9 is 3
-->> LCM of 12 and 9 is 36