C program to calculate the GCD of a number

#include<stdio.h>
#include<conio.h>
#include<process.h>
int gcd(int m,int n)
{
	int rem;
	while(n!=0)
	{
		rem=m%n;
		m=n;
		n=rem;
	}
	return(m);
}
main()
{
	int num1,num2,num3,gcd1,gcd2;
	clrscr();
	printf("Enter three positive integers");
	scanf("%d%d%d",&num1,&num2,&num3);
	if(num1==0 && num2==0 && num3==0)
	{
		printf("\n Invalid number");
		exit(0);
	}
	gcd1=gcd(num1,num2);
	gcd2=gcd(num3,gcd1);
	printf("\n GCD of %d %d %d is : %d\n",num1,num2,num3,gcd2);
	getch();
}