Question

import java.util.Scanner;
public class Test{
   public static int[] calculateFactors(int n){
      int[] array = new int[n];
      for(int i = 0; i<=n;i++){
         if(n%i==0){
            return array[i];
         }
      }
   }

   public static void main(String[] args){
      System.out.println("Please enter the number you want to find the factors for:");
      Scanner input = new Scanner(System.in);
      int n = input.nextInt();
      System.out.println(calculateFactors(n));
   }
}

I don’t understand why I get an error. I am trying to write a code where a user inputs a number and the program returns all the factors of this number.
Could anyone please tell me why when I am not being able to return the array with corresponding i factors.

Thank you

Answer 1

Look at your code (whitespace added for clarity):

public static int[] calculateFactors(int n) {
    int[] array = new int[n];
    for(int i = 0; i <= n; i++) {
        if(n % i == 0) {
            return array[i];
        }
    }
}

There are two problems:

• Your return statement doesn’t match the declared return type. You’re trying to return an int, but your method declares that it returns an int[]
• As your method is non-void, the end of the method has to be unreachable… you have to return a value through any possible path. That’s not the case with your code. What happens if n is -1? It will never go through the loop, so it will never return. More generally, the compiler will assume that (almost) any if condition may be false.

Now, as to how to fix it – given the method name, it sounds like you really do want to return all the factors… so you shouldn’t return as soon as you’ve found the first one. I’d collect the factors in a List<Integer> instead of in an array. Convert the return statement to an add call, and then return at the end of the loop. Oh, and you probably want to start the loop with i as 1 rather than 0…

All of this is specific to this particular problem though. More generally, you should look at the errors that the compiler’s giving you. They should give you all the information you need to work this out for yourself. Now that you do understand the problem, read the messages again and try to work out what stopped you from understanding it before. Could you have worked it out yourself, or were you missing some important concept?