difference between class parameter in function

Question

I wrote this code in visual studio.

public class Class1
 {
    public string MySTR;
 }


private static void func1(Class1 class )
 {
  class = new Class1();
  class.MySTR = "B";
 }

private static void func2(Class1 class )
{
  class.MySTR = "C";
}

static void Main(string[] args) 
{       
  Class1 class = new Class1();
  class.MySTR = "A";
  func1(class);
  Console.WriteLine(class.MySTR);
  func2(ref class);
  Console.WriteLine(class.MySTR);
}

I expected to get AA but I got AC.

What the difference between these methods?

Thank you.

Answer 1

Why you expect to get "AA"? "AC" is correct output. Check comments in following code blocks (codes has been modified slightly to make it compile and run) :

private static void func1(Class1 class1)
{
    //create new instance of Class1
    class1 = new Class1();
    //modify the new instance. 
    //Original instance passed to method parameter remain untouched
    //Hence you still got "A" from 1st Console.WriteLine(class1.MySTR);
    class1.MySTR = "B";
}

private static void func2(Class1 class1)
{
    //modify Class1 instance passed to method parameter. 
    //It's MySTR member value becomes "C" after this
    //Hence you got "C" from 2nd Console.WriteLine(class1.MySTR);
    class1.MySTR = "C";
}

static void Main(string[] args)
{
    Class1 class1 = new Class1();
    class1.MySTR = "A";
    func1(class1);
    Console.WriteLine(class1.MySTR);
    func2(class1);
    Console.WriteLine(class1.MySTR);
}