Try this:
using System;
public class Program
{
static void by_value(int x)
{
x = 42;
}
static void by_reference(ref int x)
{
x = 42;
}
public static void Main()
{
int i = 0;
by_value(i);
Console.WriteLine("after by_value, i = {0}", i);
by_reference(ref i);
Console.WriteLine("after by_reference, i = {0}", i);
}
}