Is prime or not

main.cpp

#include <iostream>
#include <cmath>

bool isPrime(long n) {
    long m = (long)sqrt(n);
    if (m != 2) {
        while (m > 2){
            if(n % m == 0) {
                return false;
            }
            else {
                --m;
            }
        }
    }
    else if (n % m == 0)
        return false;
    else
        return true;
}

int main(int argc, char **argv) {
    long num;
    std::cout << "Please enter a number: " << std::endl;
    std::cin >> num;
    if (isPrime(num) == true)
        std::cout << "The number is prime." << std::endl;
    else
        std::cout << "The number is divisable!" << std::endl;
    return 0;
}