understanding C# Code

Question

Can someone explain me that code in detail? I dont get it:

class Program
{
static int Sum(int x)
{
if (x != 0)
{
return x + Sum(x - 1);
}

else
return x;
}

static void Main(string[] args)
{
int x = 6;
x = Sum(x);
Console.WriteLine(++x);
Console.ReadKey();
}
}
}

Answer 1

I wrote the code on visual studio and I get 22. I also Start Debugging but finally the solution is 22.

Answer 2

return x + sum(x-1)

return 6 + sum(6-1)
return 5 + sum(5-1)
...
return 1 + sum(1-1)

and when x == 0

return x;

in other word function sum runs while x != 0
and when x == 0 stops running.

output ++x means 1

Answer 3

kewl

Answer 4

Yes because see

x = sum(x)

so x = 6 + 5 + 4 + 3 + 2 + 1 = 21

++x = 22

sorry i forget about
this line

x = Sum(x);