simplest way of computing primality. Know if a number is prime. Slowest way

02.esprimo_simple.cpp

// 02.esprimo_simple.cpp
// juanfc 2009-10-16
#include <iostream>
using namespace std;

int main()
{
    cout << "Please enter an integer: ";
    int n;
    cin >> n;

    int i = 2;
    while (i < n and n % i != 0) // is necessary i<n?
        ++i;

    if (i >= n)
        cout << "YES, it is prime" << endl;
    else
        cout << "NO, it is not a prime" << endl;

    return 0;
}