Write a C program to find the GCD of two numbers

Here is a C program ....
#include <stdio.h>
int gcd(int a, int b);
int gcd_recurse(int a, int b);
int main()
{
printf("\nGCD(%2d,%2d) = [%d]", 6,4, gcd(6,4));
printf("\nGCD(%2d,%2d) = [%d]", 4,6, gcd(4,6));
printf("\nGCD(%2d,%2d) = [%d]", 3,17, gcd(3,17));
printf("\nGCD(%2d,%2d) = [%d]", 17,3, gcd(17,3));
printf("\nGCD(%2d,%2d) = [%d]", 1,6, gcd(1,6));
printf("\nGCD(%2d,%2d) = [%d]", 10,1, gcd(10,1));
printf("\nGCD(%2d,%2d) = [%d]", 10,6, gcd(10,6));
printf("\nGCD(%2d,%2d) = [%d]", 6,4, gcd_recurse(6,4));
printf("\nGCD(%2d,%2d) = [%d]", 4,6, gcd_recurse(4,6));
printf("\nGCD(%2d,%2d) = [%d]", 3,17, gcd_recurse(3,17));
printf("\nGCD(%2d,%2d) = [%d]", 17,3, gcd_recurse(17,3));
printf("\nGCD(%2d,%2d) = [%d]", 1,6, gcd_recurse(1,6));
printf("\nGCD(%2d,%2d) = [%d]", 10,1, gcd_recurse(10,1));
printf("\nGCD(%2d,%2d) = [%d]", 10,6, gcd_recurse(10,6));
getch();
return(0);
}
// Iterative algorithm
int gcd(int a, int b)
{
int temp;
while(b)
{
temp = a % b;
a = b;
b = temp;
}
return(a);
}
// Recursive algorithm
int gcd_recurse(int a, int b)
{
int temp;
temp = a % b;
if (temp == 0)
{
return(b);
}
else
{
return(gcd_recurse(b, temp));
}
}
And here is the output ...
Iterative
----------------
GCD( 6, 4) = [2]
GCD( 4, 6) = [2]
GCD( 3,17) = [1]
GCD(17, 3) = [1]
GCD( 1, 6) = [1]
GCD(10, 1) = [1]
GCD(10, 6) = [2]
Recursive
----------------
GCD( 6, 4) = [2]
GCD( 4, 6) = [2]
GCD( 3,17) = [1]
GCD(17, 3) = [1]
GCD( 1, 6) = [1]
GCD(10, 1) = [1]
GCD(10, 6) = [2]

Note that you should add error handling to check if someone has passed negative numbers and zero.