#include <ctype.h>

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

  for ( i= 0; isspace(s[i]); i++)
    ;
  sign = (s[i] == '-') ? -1 : 1;
  if ( s[i] == '+' || s[i] == '-')
    i++;
  for ( val = 0.0; isdigit(s[i]); i++)
    val = 10.0 * val + (s[i] - '0');
  if ( s[i] == '.')
    i++;
  for ( power = 1.0; isdigit(s[i]); i++)    {
      val = 10.0 * val + ( s[i] - '0' );
      power *= 10.0;
    }
  return sign * val /power;
 }