Basic Prime Checker, C++

 1#include <iostream>
 2#include <cmath>
 3
 4using std::cout;
 5using std::cin;
 6
 7int main() {
 8
 9  int myNumber = 0;
10  bool prime = true;
11
12  //The user is prompted to input a positive integer.
13  cout << "Input a positive integer: ";
14  //The user inputs a positive integer.
15  cin >> myNumber;
16
17  /*
18  * The program checks for special cases at the beginning to simplify the process.
19  * If the number is divisible by any single-digit prime, the number is not prime.
20  */
21  if(myNumber == 0 || myNumber == 1){prime = false;}
22  if ( myNumber > 2 && myNumber % 2 == 0 ) {prime = false;}
23  if ( myNumber > 3 && myNumber % 3 == 0 ) {prime = false;}
24  if ( myNumber > 5 && myNumber % 5 == 0 ) {prime = false;}
25  if ( myNumber > 7 && myNumber % 7 == 0 ) {prime = false;}
26
27  //If the number passes that test, continue checking.
28  if(prime){
29    /*
30    *The program only needs to check up to the square root of myNumber because
31    * if myNumber is not prime, it can be factored into i*i.
32    */
33    for (int i = sqrt(myNumber); i > 3; i--)
34    {
35      if(prime){
36        if(myNumber % i == 0){
37          prime = false;
38        }
39      }else{
40        //No need to keep looping if we've already determined it's not prime.
41        break;
42      }
43    }
44  }
45
46  //Feedback to the user before the program ends.
47  if(prime){
48    cout << myNumber << " IS prime!";
49  }
50  else{
51    cout << myNumber << " is NOT prime!";
52  }
53
54  return 0;
55}