Answer S9

/* Puzzle S09 --  Convert a string to an int */

#include <stdio.h>
#include <stdlib.h>

int stringToInt( char *p )
{
  int value = 0;
  int multiplier = 1;  /* change to -1 if string starts with minus */

  if ( *p == '+' ) p++;
  if ( *p == '-' )
  {
    multiplier = -1;
    p++ ;
  }
  while ( *p>='0' && *p<= '9' )
  {
    value *= 10;
    value += *p - '0';
    p++ ;
  }
  return value*multiplier;
}

int main()
{
  char *trials[] =
  {
   "1",
   "12",
   "+1",
   "-8",
   "+2003",
   "-345",
   "12o5",
   "rats",
   "-oh dear",
   "+ 234 ",
   "++45"
  };

  int j ;
  for ( j=0; j<sizeof(trials)/sizeof(char *); j++ )
  {
    printf("%s is converted into: %d\t\tshould be: %d\n", trials[j],
         stringToInt( trials[j]), atoi( trials[j]) );
  }

  return 0;
}