Example of weakness of -Werror=return-type in gcc

gistfile1.c

#include <stdio.h>
#include <stdbool.h>

bool f(char achar) {
  switch (achar)
    {
    case 'q':
      return true;
      break;
    case 'w':
      return false;
      break;
    }
  //We shouldn't be here
}

int main() {
  printf("Enter a character\n");
  char input = getchar();

  /*
  if ( !( input == 'q' || input == 'w') ) {
      input = 'w';
    }
  */

  bool output = f(input);

  if ( output )
    { 
      printf("You entered q\n");
    }
  else
    {
      printf("You entered w\n");
    }
  return 0;
}

So, what happens when the user enters d?

Well, undefined behaviour as per my comment from 2014.