Beginner C Programmer needs help with pointers ( I think )

#include <stdio.h>
int greatestCD (int num1, int num2);

int main(void)
{
    int a=0, b=0;
    int result;
    printf("Please enter two numbers to calculate the greatest common denominator fromn");
    scanf("%d%d", &a, &b);
    result = greatestCD (a,b);
    printf("Using the correct in main way:nThe greatest common denominator of %d and %d is %dn",a,b, result);
}

int greatestCD (int num1 ,int num2)
{

    if (num2==0){
        printf("Using the cheaty in gcd function way:nThe greatest common denominator is %dn",num1);
        return num1;
    } else {
        greatestCD(num2,(num1%num2));
    }
}

C:UsersSamDocumentsC programs>gcd
Please enter two numbers to calculate the greatest common denominator from
12
15
Using the cheaty in gcd function way:
The greatest common denominator is 3
Using the correct in main way:
The greatest common denominator of 12 and 15 is 2293524

greatestCD(num2,(num1%num2));

return greatestCD(num2,(num1%num2));

/dev/shm $ gcc x.c
/dev/shm $ ./a.out
Please enter two numbers to calculate the greatest common denominator from
12
15
Using the cheaty in gcd function way:
The greatest common denominator is 3
Using the correct in main way:
The greatest common denominator of 12 and 15 is 3
/dev/shm $ gcc --version
gcc (Debian 4.3.2-1) 4.3.2
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.