Passing by Value and by Reference

using System.IO;
using System;

class Program
{
    int a = 10;
    int b = 20;
    string str1 = "before";
    string str2 = "after";
    
    private void DisplayNumbers(string txt, int int1, int int2)
    {
        Console.WriteLine("Numbers {0} swap : a = {1}, b = {2} ", txt, int1, int2);
    }
    
    private void SwapByValue(int int1, int int2)
    {
        Console.WriteLine("SwapbyValue is called.");
        int temp = int1;
        int1 = int2;
        int2 = temp;
    }
    
    private void SwapByRef(ref int int1, ref int int2)
    {
        Console.WriteLine("SwapbyRef is called.");
        int temp = int1;
        int1 = int2;
        int2 = temp;
    }
    
    static void Main()
    {
        Program p = new Program();
        
        p.DisplayNumbers(p.str1, p.a, p.b);
        p.SwapByValue(p.a,p.b);
        p.DisplayNumbers(p.str2, p.a, p.b);
        Console.WriteLine();
        
        p.DisplayNumbers(p.str1, p.a, p.b);
        p.SwapByRef(ref p.a,ref p.b);
        p.DisplayNumbers(p.str2, p.a, p.b);
    }
}