Question

How does the following piece of code work, in other words what is the algorithm of the C preprocessor? Does this work on all compilers?

#include <stdio.h>

#define b a
#define a 170


int main() {
  printf("%i", b);
  return 0;
}

Answer 1

The preprocessor just replaces b with a wherever it finds it in the program and then replaces a with 170 It is just plain textual replacement.

Works on gcc.