java program

public class Main {

public static void main(String[] args) {

int num = 13;
boolean flag = false;
for (int i = 2; i <= num / 2; ++i) {
  // condition for nonprime number
  if (num % i == 0) {
    flag = true;
    break;
  }
}

if (!flag)
  System.out.println(num + " is a prime number.");
else
  System.out.println(num + " is not a prime number.");

}
}