Answer to Question #125070 in C++ for Zeeshan Ali

Question

: Write program that prompts the user to input a positive integer. It should then output a message indicating whether the number is a prime number. (Note: An even number is prime if it is 2. An odd integer
is prime if it is not divisible by any odd integer less than or equal to the square root of the number.)

Answer 1

#include <iostream>


int main()
{
    std::cout << "Please input a positive integer: ";
    int number;
    std::cin >> number;


    if(number < 0)
    {
        std::cout << "Error: integer is negative\n";
        return 1;
    }


    if(number < 2)
    {
        std::cout << "Integer is not prime\n";
        return 0;
    }


    if(number == 2)
    {
        std::cout << "Integer is prime\n";
        return 0;
    }


    if(number % 2 == 0)
    {
        std::cout << "Integer is not prime\n";
        return 0;
    }


    for(int i=3; (i*i)<=number; i+=2)
    {
        if(number % i == 0)
        {
            std::cout << "Integer is not prime\n";
            return 0;
        }
    }


    std::cout << "Integer is prime\n";
    return 0;
}