int x = 10; x += x--; in .Net - Why?

Question

int x = 10; x += x--; 

In C#/.Net, why does it equal what it equals? (I'm purposely leaving the answer out so you can guess and see if you're right)

Answer 1

Look at this statement:

x += x--; 

This is equivalent to:

x = x + x--; 

Which is equivalent to:

int a1 = x; // a1 = 10, x = 10 int a2 = x--; // a2 = 10, x = 9 x = a1 + a2; // x = 20 

So x is 20 afterwards - and that's guaranteed by the spec.

What's also pretty much guaranteed, although not by the spec, is that anyone using such code will be attacked by their colleagues. Yes, it's good that the result is predictable. No, it's not good to use that kind of code.