Question

Can someone tell me how prefix / postfix operators really work? I’ve been looking online a lot but haven’t found anything.

From what I can tell prefex first increments, then does the operation and then assigns.
Postfix would do the operation first, then assign and then increment.

But I’m having a bit of trouble with my code:

int x, y;
x = 1;
y = x + x++; // (After operation y = 2)(x=2)

However when I do:

y = x++ + x; // (After operation y = 3)(x=2)

I’m not sure why these operations would be any different. I have two questions:

• Could you explain the difference?

• How does this apply to the other operator Prefix?

Answer 1

• In C# the operands of + are evaulated in left-to-right order.
• In C and C++ the order of evaluation for the operands of + is unspecifed.

For C# your examples work as follows:

 y = x + x++;
     ^ x is 1
         ^ x is increased to 2, but the postfix increment returns the old value (1)
 y = 2

 y = x++ + x;
     ^ x becomes 2, but postfix increment returns the old value (1)
           ^ x is now 2 here
 y = 3