Why does sizeof(x++) not increment x?

Question

Here is the code compiled in dev c++ windows:

#include <stdio.h>  int main() {     int x = 5;     printf("%d and ", sizeof(x++)); // note 1     printf("%d\n", x); // note 2     return 0; } 

I expect x to be 6 after executing note 1. However, the output is:

4 and 5 

Can anyone explain why x does not increment after note 1?

Answer 1

From the C99 Standard (the emphasis is mine)

6.5.3.4/2

The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. The size is determined from the type of the operand. The result is an integer. If the type of the operand is a variable length array type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an integer constant.