Question

I dont really understand what the last while loop is doing, can someone explain it?

void reverse(char *str) { 
    char * end = str; 
    char tmp; 

    if (str) {
        while (*end) { 
            ++end;
        }
        --end; 
        while (str < end) {
            tmp = *str; 
            *str++ = *end;
            *end-- = tmp;
        }
    }
}

Can someone walk me through the example “hello”?

Answer 1

What’s basically happening in that innermost while loop is that in each iteration, the characters pointed to by str and end get swapped, str gets incremented to point to the next character, and end is decremented to point to the previous one.

Using “hello” as an example:

v   v
hello
 v v 
oellh
  v
olleh

And then the loop ends, as str = end.