Call by Reference And Call by value

Question

HiPlz have luk @Below code:- plz explain me .....whether its call by Call by Reference Or Call by value class Program { public static void Input(string C) { C= ABCD; Console.WriteLine(C); } static void Main(string[] args) { string B = EFGH; Program.Input(B); Console.ReadKey(); } } Output : ABCD 1)Looking at the example it shows its call by value becoz  if we use call by refrence then we have to use ref keyword which is not in this case so its call by value according me. 2)But then if it is call by value it should print EFGH but rather its printing ABCD of input method . Why plz explain.. Thnx in Advance

Vulpes · Answer

The local variable B contains a reference to the string EFGH. When this variable is passed by value to the Input method the parameter C receives a copy of this reference. Consequently both B and C refer to the string EFGH when the method starts. However C is assigned a reference to the string ABCD within the body of the method and this value is then printed to the console. This assignment to C doesn't change B which still refers to EFGH. So when the method returns and the value of B is printed to the console it's still EFGH. It's important to realize that B and C represent different memory locations and so are independent of each other once the method is called.

Aman Jen · Answer

Thnx for your reply...but ideally it shuld print EFGH..if its call by value..I am not getting the reason for that.....

Vulpes · Answer

I've just extended your example a bit to make this clearer: using System; class Program { public static void Input(string C) { C = ABCD; Console.WriteLine(C); } public static void Input(ref string C) { C = ABCD; Console.WriteLine(C); } static void Main(string[] args) { string B = EFGH; Program.Input(B); Console.WriteLine(B); // still EFGH as change not persisted Program.Input(ref B); Console.WriteLine(B); // now ABCD as call by reference Console.ReadKey(); } } The output is: ABCD EFGH ABCD ABCD

Vulpes · Answer

Yes it is 'call by value'. However this doesn't prevent you from changing the value parameter within the method and printing it out. The difference is that the change won't be persisted to the calling code as it would with a call by reference.