int my_atoi(const char *str)

 {

     assert(str != NULL);

     int flag = ;

     int result = ;

     while(*str == ' ' || *str == '\n' || *str == '\t')

     {

         ++str;

     }

     if(*str == '-')

     {

         flag = -;

         ++str;

     }

     else if(*str == '+')

     {

         ++str;

     }

     while(*str != '\0')

     {

         if(*str >= '' && *str <= '')

         {

             result = result* + *str - '';

         }

         else

         {

             return flag * result;

         }

         ++str;

     }

     return flag * result;

 }