Discussion

What is the output for the following code snippet?

#include <stdio.h>
#define A -B
#define B -C
#define C 5

int main()
{
  printf("The value of A is %d\n", A); 
  return 0;
}

Answer: B

Correct answer: The value of A is 5

Macros are rescanned after expansion, so the substitution cascades:

A → -B → -(-C) → -(-5)

Two negations cancel, so the value printed is 5.

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