Difference between Call by value & Call by reference

Call by value :
using System;

namespace call_by_value
{
	class c
	{
		 public int x=100;
		 public void method(int x)
		 {
			 x=x+x;
			 Console.WriteLine("within the method : "+x.ToString());
		 }
		 public static void Main()
		{
			 c obj=new c();
			 Console.WriteLine(obj.x);
			 obj.method(obj.x);
			 Console.WriteLine("after coming out of the method : "+obj.x);
			 Console.ReadLine();
		 }
	}
}

using System;
namespace call_by_reference
{
	class c
	 {
		 public int x=100;
		 public void method(ref int x)
		 {
			 x=x+x;
			 Console.WriteLine("within the method : "+x.ToString());
		 }
		 public static void Main()
		 {
			 c obj=new c();
			 Console.WriteLine(obj.x);
			 obj.method(ref obj.x);
			 Console.WriteLine("after coming out of the method : "+obj.x);
			 Console.ReadLine();
		 }
	}

}