TheAlgorithms-C-Plus-Plus/math/check_prime.cpp

/**
 * Copyright 2020 @author omkarlanghe
 *
 * @file 
 * A simple program to check if the given number if prime or not.
 * 
 * @brief
 * Reduced all possibilities of a number which cannot be prime.
 * Eg: No even number, except 2 can be a prime number, hence we will increment our loop with i+2 jumping on all odd numbers only.
 * If number is <= 1 or if it is even except 2, break the loop and return false telling number is not prime.
 */
#include <iostream>
#include <cassert>
 /**
 * Function to check if the given number is prime or not.
 * @param num number to be checked.
 * @return if number is prime, it returns @ true, else it returns @ false.
 */
template<typename T>
bool is_prime(T num) {
    bool result = true;
    if (num <= 1) {
        return 0;
    } else if (num == 2) {
        return 1;
    } else if ((num & 1) == 0) {
        return 0;
    }
    if (num >= 3) {
        for (T i = 3 ; (i*i) < (num) ; i = (i + 2)) {
            if ((num % i) == 0) {
                result = false;
                break;
            }
        }
    }
    return (result);
}

/**
 * Main function
 */
int main() {
    int num;
    std::cout << "Enter the number to check if it is prime or not" <<
    std::endl;
    std::cin >> num;
    bool result = is_prime(num);
    if (result) {
        std::cout << num << " is a prime number" <<
        std::endl;
    } else {
        std::cout << num << " is not a prime number" <<
        std::endl;
    }
    assert(is_prime(50) == false);
    assert(is_prime(115249) == true);
}