// include necessary libraries
// those are required for some types to work.
#include <iostream>


using namespace std;

int main()
{
    //declaring required variables.
    int num = 0;
    int c_prime = 0;


    //prompting user for inputs.
    cout << "Please enter an integer greater than 1 : " << endl;
    cin >> num;
    //extra line for spacing.
    cout << endl;
                            //if the user happens to input a value less than 1, let him/her knows.
                            //because this program was meant to find prime from 1.
                            if(num<1){
                                cout << "You will have to enter a number greater than 1, sorry.";

                            }
                                //goes only if the user input, num is greater than 1.
                                while(num >1){

                                    //starts a for loop where d_num is assigned as num decreasing by 1 and as a decrementing value.
                                    for(int d_num = (num-1); d_num>1; d_num--){

                                        //assign the value of num to d_num.
                                        //where num will keep decreasing and
                                        //do a series of check to see if it's prime or not.
                                        num = d_num;

                                    //2 is a prime exception where it is the only even number.
                                    //we also know it is always prime.
                                    //this will output num if and when it becomes 2 before or after doing the loop
                                    //at least once.
                                    if(num ==2){
                                        cout << num << " is a prime number." << endl;
                                    }

                                    //c_prime is the remainder after dividing num by 2.
                                    //to check if it is divisible by 2.
                                    //there are not any prime numbers that is even except 2.
                                    c_prime = num%2;

                                    //this if loop runs if there is the remainder is not 0,
                                    //that means that this number,num might be a prime number.
                                    if(c_prime != 0){

                                        for(int d_num = (num-1); d_num >2; d_num--){

                                        //assign c_prime the value of the remainder of num divided by d_num, which is
                                        //a decreasing set of numbers starting from the value of num.
                                        c_prime = num%d_num;

                                        //check if the number, num has no remainder.
                                        //means that number is absolutely not a prime number.
                                        //and it will break the loop, starting program from top.
                                         if(c_prime == 0){
                                            break;
                                         }
                                        }

                                        //final check, checking if the number, num
                                        //has a remainder where c_prime will be greater than 0.
                                        //this means the num here is prime.
                                        if(c_prime !=0){

                                        //print out the prime number.
                                        cout << num << " is a prime number." << endl;

                                        //another case, if the value of c_prime at this point is 0,
                                        //it is absolutely not a prime number.
                                        //and this break the loop.
                                        }else if(c_prime == 0){
                                                 break;
                                                 }
                                                //break the loop so that it starts checking other numbers.
                                                 break;

                                    }
                                }
                            }

    return 0;
}