Passing By Value Vs By Ref C#

A value-type variable contains its data directly as opposed to a reference-type variable, which contains a reference to its data. Passing a value-type variable to a method by value means passing a copy of the variable to the method. Any changes to the parameter that take place inside the method have no affect on the original data stored in the argument variable. If you want the called method to change the value of the parameter, you must pass it by reference, using the ref or out keyword. For simplicity, the following examples use ref.

Value Types

Bool, byte, char, decimal, double, enum, float, int, long, sbyte, short, struct, uint, ulong, ushort

Reference Types

Class, delegate, dynamic, interface, object, string

C# Example

private void button1_Click(object sender, EventArgs e)

{

     int i = 100;

     PassByVal(i);   // Don't change original value

     button1.Text = i.ToString(); // OutPut is : 100

     PassByRef(ref i);   // Change original value

     button1.Text = i.ToString(); // OutPut is : 110

}

private void PassByRef(ref int i) { i += 10; }

private void PassByVal(int i) { i += 10; }

More Difference

http://csharptopicwiseques.blogspot.com/2010/08/value-type-and-reference-types.html

Value Type	Reference Type
They are stored on stack	They are stored on heap
Contains actual value	Contains reference to a value
Cannot contain null values. However this can be achieved by nullable types	Can contain null values.
Value type is popped on its own from stack when they go out of scope.	Required garbage collector to free memory.
Memory is allocated at compile time	Memory is allocated at run time