how to check if a number is prime cpp code example

Example 1: check prime in c++

#include <bits/stdc++.h>
#include <math.h>
using namespace std;

#define ll long long

bool checkPrime(int number){
	for(int i=2; i<=sqrt(number); i++){
		if(number%i==0){
			return false;
		}
	}
	return true;
}

Example 2: C++ prime number check

// 6k+-1 optimisation
bool is_prime6(int num) {
  int i;
  if (num == 1)
    return false;
  if (num <= 3)
    return true;
  if (num % 2 == 0 || num % 3 == 0)
    return false;
  if (num < 25)
    return true;
  for (i = 5; i * i <= num; i += 6)
    if (num % i == 0 || num % (i + 2) == 0)
      return false;
  return true;
}