jbm@jbm.nada.kth.se (Jonas M�ls�) writes:

> 	Also, I have never encountered a real situation
> 	where I have needed an extra flag in the predicate.
> 	One can actually do fine without them. As an example,
> 	I hereby present to you three variations of str_index.
> 
> 	The first one strictly exits at the top. The other two
> 	in the middle. The first one is much easier to reason 
> 	about, and to understan, IMHO. Anyway, introducing an
> 	extra flag in the predicate is very often a sign of
> 	"patching the loop". Done right, one does not need it.
> 
> 
> 
> /** str_index
>  *
>  * str_index returns a pointer to the first occurrence of
>  * the given character in the given string.
>  * If the given character does not occur in the given
>  * string, str_index returns NULL.
>  * 
>  * If the given pointer is NULL, the result is undefined.
>  * 
>  */
> 
> 

Here's another idea:

char *
str_index (
    char   *s,			/* string to search           */
    char    c)			/* character to search for    */
{
    for (;;)
        if (*s == c)
           return s;
        
        else if (*s == '\0')
           return NULL;

        else
           s++;
}

I don't know if this is typical C code, however.  I suspect one would
move some of the work up into the for loop declaration:

   for (; *s != '\0'; s++)
      if (*s == c) 
         return s;

   return NULL;


An Ada programmer has an easier go of it:

function Get_Position (S : String; C : Character) return Natural is
begin
   for Index in S'Range loop
      if S(Index) = C then
         return Index;
      end if;
   end loop;
  
   return 0;
end Get_Position;