How to get difference between two array without using linq or Set operator using csharp ?

using System;

class Program
{
	public static void Main(string[] args)
	{
		string[] a = {"Watermelon", "Apple", "Mango", "Guava", "Banana"};
		string[] b = {"Orange", "Kiwi", "Apple", "Watermelon"};

		Console.WriteLine("Differences:\n");	
		int numDiff = arrayDifference(a, b);
		string diffResult = numDiff == 0 ? "There are no differences" : "Number of differences found: " + numDiff;
		Console.WriteLine("\n" + diffResult + "\n");
		
		Console.Write("Press any key to continue . . . ");
		Console.ReadKey(true);
	}
	
	static int arrayDifference(string[] x, string[] y) {
		int numberOfDifferentElements = 0;
		
		foreach(string s in x) {
			if (Array.IndexOf(y, s) == -1) {
				Console.WriteLine(s);
				numberOfDifferentElements++;
			}
		}
		
		foreach(string s in y) {
			if (Array.IndexOf(x, s) == -1) {
				Console.WriteLine(s);
				numberOfDifferentElements++;
			}
		}
		
		return numberOfDifferentElements;
	}
}

Differences:

Mango
Guava
Banana
Orange
Kiwi

Number of differences found: 5

Press any key to continue . . .