In C#, string is a reference type but why it's not changing after manipulating it in another method [duplicate]

Answer 1

This has nothing to do with string being a reference type. This is because the parameter is passed by value, not by reference.

If you modify your method like this, so that the parameter is passed by reference:

public static void Test(ref string testString)
{
    testString = "Modified Value";
}

Then sample will be modified.

See this article for more details about parameter passing.

Answer 2

That's because of way how CLR passes the params to method.

Put simply:

string sample = "Initial value";  

Here sample variable refers to "Initial value" string instance stored in heap.

public static void Test(string testString) 
{ 
    testString = "Modified Value"; 
}

In the method you modify testString variable(copy of sample variable) making it references to "Modified Value" string in a heap, leaving original sample variable no affected.