brilliant.c

#include "brilliant.h"
#define true 1
#define false 0

int gcd(int a, int b) {
  int c;
  while (a!=0) {
    c=a; 
    a=b%a;  
    b=c;
  }
  return b;
}

int gcd3(int a, int b, int c) {
	return gcd(gcd(a,b),c);
}

int reverse(int n) {
        int result = 0;
        while (n > 0) {
            result = result * 10 + n%10;
            n = n/10;
        }
        return result;
}

int isPrime(int n) {
	int i;
	for (i=1; i<n; i++) {
		if (n % i == 0 && i!=1) {
			return false;
		}
	}
	return true;
};

brilliant.h

#ifndef BRILLIANT_H
#define BRILLIANT_H

//greatest common divisor
int gcd(int a, int b);
int gcd3(int a, int b, int c);


//reverse integer
int reverse(int n);

//is prime
int isPrime(int n);

#endif