Tells if number is prime or not.
Ask questions if you have them.


#include <iostream.h>

#include <math.h>



int main()

{

    int num, x=0;

    

    cout<<"Enter a number: ";

    cin>>num;

    while(num<2)//deals with incorrect user input

    {

         cout<<"No, a number larger than 1."<<endl;

         cout<<"Try again: ";

         cin>>num;

    }

	for (int i=2; i<=sqrt(num)&&x==0; i++)// basically saying divide your number by 2, then 3, so on.

	 {		         //sqrt because you only need to check first half of the numbers of the inputted number

		if (num % i == 0)//if at any time, the number divides perfectly, it's not prime

		{

            x=num; //this breaks the loop

			cout << "It is not prime number." << endl;

			cout<<num<<"/"<<i<<"= "<<num/i<<endl;

		}

	 }

	 if(x==0)//if the value we've set as x is still zero, nothing was divided perfectly, it's prime.

	 {

             cout<<"Yes, that's a prime number."<<endl;

     }



system ("PAUSE");

return 0;

}