Question

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C#: what is the difference between i++ and ++i?

I see this operator (++) very often. I know what it does ultimately, but it seems like there’s some rules I don’t understand. For example, it seems to matter if you put it before or after the variable you’re using it on. Can someone explain this?

Answer 1

The statement

x++;

is exactly equivalent to

x = x + 1;

except that x is evaluated only once (which makes a difference if it is an expression involving property getters).

The difference between the following two:

DoSomething(x++);   // notice x first, then ++
DoSomething(++x);   // notice ++ first, then x

Is that in the first one, the method DoSomething will see the previous value of x before it was incremented. In the second one, it will see the new (incremented) value.

For more information, see C# Operators on MSDN.

It is possible to declare a custom ++ operator for your own classes, in which case the operator can do something different. If you want to define your own ++ operator, see Operator Overloading Tutorial on MSDN.