Difference between pre- and postfix incrementation in C (++a and a++)

Question

As far as I understand, a++ is postfix incrementation, it adds 1 to a and returns the original value. ++a is prefix incrementation, it adds 1 to a ad returns the new value.

I wanted to try this out, but in both cases, it returns the new value. What am I misunderstanding?

#include <stdio.h>
int main() {
  int a = 0;
  int b = 0;

  printf("%d\n", a); // prints 0
  printf("%d\n", b); // prints 0

  a++; // a++ is known as postfix. Add 1 to a, returns the old value.
  ++b; // ++b is known as prefix. Add 1 to b, returns the new value.

  printf("%d\n", a); // prints 1, should print 0?
  printf("%d\n", b); // prints 1, should print 1

  return 0;
}

Answer 1

Remember, C and C++ are somewhat expressive languages.

That means most expressions return a value. If you don't do anything with that value, it's lost to the sands of time.

The expression

(a++)

will return a's former value. As mentioned before, if its return value is not used right then and there, then it's the same as

(++a)

which returns the new value.

printf("%d\n", a++); // a's former value
printf("%d\n", ++b); // b's new value

The above statements will work as you expect, since you're using the expressions right there.

The below would also work.

int c = a++;
int d = ++b;

printf("%d\n", c); // a's former value
printf("%d\n", d); // b's new value