-atof- function , example from section 4.2 K&R2

This is the example from section 4.2, page 71 of K&R2:


double atof( char s[] )
{
  int i, sign;
  double val, power;


  for( i = 0; isspace( s[i] ); ++i )
    {
      /* skipe the leading whitespace */
    }
  
  sign = ( (s[i] == '-') ? -1 : 1 );

  if( s[i] == '+'|| s[i] == '-' )
    {
      ++i;
      /* skip the leading sign, of any */
    }
  
  for( val = 0.0; isdigit( s[i] ); ++i )
    {
      val = (10.0 * val) + (s[i] - '0');
      
      /* s[i] - '0' (zero in quotes)
       * always gives "int i" as output
       */
    }

  if( s[i] == '.' )
    {
      ++i;
      /* skip the dot(.) of a floating point */
    }

  for( power = 1.0; isdigit( s[i] ); ++i )
    {
      val = (10.0 * val) + (s[i] - '0');
      power *= 10.0;
    }

  return sign * val / power;
}


I can't really think of that kind of clever-tricks shown here. checking
for leading space and dot (.) are fine,they are very general things and
easily come to my mind but look at how cleverly the K&R created the
expressions  like (val = 10.0 * val) and (power *= 10.0). these loops
using variables "val" and "power" are pretty much the work of people with
high IQs.  After some work I can understand them but I can not create them
at very 1st place, I dont have that kind of thinking.

These tricks never came to my mind. Is this what we call programming ? if
yes, it is pretty much harder to come to my mind, may be never. I just do
not think this way.