/*
CSE 142, Autumn 2007, Marty Stepp

This is a new version of our previous Factors program that uses "Boolean Zen."

Boolean Zen means understanding why the following are never needed,
    == true
    == false
    != true
    != false
and also understanding why the one-line version of isPrime below is the same
as the previous multi-line version.
*/

import java.util.*;   // for Scanner

public class Factors4 {
    public static void main(String[] args) {
        if (isPrime(17)) {
            System.out.println("17 is a prime number.");
        }
        if (!isPrime(42)) {
            System.out.println("42 isn't a prime number.");
        }
    }
    
    // Returns whether the given integer is a prime number
    // (whether it has only itself and 1 as factors).
    public static boolean isPrime(int n) {
        return countFactors(n) == 2;
    }

    // Returns whether the given integer is a composite (non-prime) number.
    public static boolean isComposite(int n) {
        // return countFactors(n) != 2;
        // return isPrime(n) == false;
        return !isPrime(n);
    }

    // Returns how many factors the given number has.
    // Assumes n is non-negative.
    public static int countFactors(int n) {
        int count = 0;
        for (int i = 1; i <= n; i++) {
            if (n % i == 0) {
                // i is a factor of n
                count++;
            }
        }
        return count;
    }
}