Question

Possible Duplicate:
Why does sizeof(x++) not increment x?

#include<stdio.h>
int main(void)
{
  double num=5.2;
  int var=5;
  printf("%d\t",sizeof(!num));
  printf("%d\t",sizeof(var=15/2));
  printf("%d",var);
  return 0;
}

The program gave an output 4 4 5. I didn’t quite get why this happened.

• Why was the first output 4?
• Why didn’t the value of var get updated to 7?

How does the sizeof operator work?

Answer 1

The expressions

!num
var=15/2

both evaluate to an int. sizeof(int) is always 4 on your platform.

As for why var is not updated:

sizeof is a compile-time operator, so at the time of compilation sizeof and its operand get replaced by the result value. The operand is not evaluated (except when it is a variable length array) at all; only the type of the result matters.

https://stackoverflow.com/a/8225813/141172