Determine if a number is prime. If it is not, then display its largest factor

/*
C#: The Complete Reference
by Herbert Schildt

Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
/*
Determine if a number is prime. If it is not,
then display its largest factor.
*/

using System;

public class FindPrimes {
public static void Main() {
int num;
int i;
int factor;
bool isprime;

for(num = 2; num < 20; num++) { isprime = true; factor = 0; // see if num is evenly divisible for(i=2; i <= num/2; i++) { if((num % i) == 0) { // num is evenly divisible -- not prime isprime = false; factor = i; } } if(isprime) Console.WriteLine(num + " is prime."); else Console.WriteLine("Largest factor of " + num + " is " + factor); } } } [/csharp]