How to work with a Boolean function in C in this code

Question

What is wrong in this code?

#include <stdio.h>

bool func(char *, int);

void main()
{
   char *a = "Interview";
   if(func(a, 9))
   {
      printf("True");
   }
   else
   {
      printf("False");
   }
}

bool func(char *s, int len)
{
   if(len < 2)
      return true;
   else
      return s[0] == s[len-1] && func(&s[1], len-2);
}

I believe this function always returns TRUE. This is an interview question. But, when I try to compile this, it shows six errors...

Answer 1

I'm going to guess it doesn't know what bool and true are. bool is not a primitive data type in C. You need an extra include:

#include <stdbool.h>

The second part of your question? Does it always return TRUE?

No:

When you come into the function, you'll skip the first return because your length is 9. So instead you'll return if true only if:

return s[0] == s[len-1] && func(&s[1], len-2)

Is true. You can skip the recursive logic here because it's not modifying your string. Just look at the first part:

s[0]     // This has to be 'I'
==       // We need so what we compare against has to be 'I' as well
s[len-1] // This will be 'w'

So... that's not going to return true... Who cares about ANDing (&&) the recursive part? I suspect the compiler will even optimize that out because everything here is hard coded.