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

Question

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

#include 

int main() {
    int x = 5;
    printf(\"%d and \", sizeof(x++)); // note 1
    print         


        

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.