how to check prime number cpp code example

Example 1: 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;
}

Example 2: check prime in c++

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

#define ll long long
bool isPrime(ll number){
	  for(ll i = 2; i <= number / 2; i++){
	  
  
      	if(number % i == 0)
      {
          return false;
          break;
      }
 	}
 	
 	return true;
}