my_getnbr

my_getnbr.c

#include <stdio.h>

#define my_getnbr(str) my_getnbr_rec(str, 0, 1, 0)

long int my_getnbr_rec(const char *str, long int nbr, char sign, char began)
{
  if (*str == '-' && !began)
    sign *= -1;
  else if (*str >= '0' && *str <= '9' && (began = (*str != '-' && *str != '+'))) {
    nbr *= 10;
    nbr += *str - '0';
  } else if (*str != '+')
    return (nbr * sign);
  return (my_getnbr_rec(++str, nbr, sign, began));
}

int main()
{
        printf("%ld\n", my_getnbr("42"));
        printf("%ld\n", my_getnbr("0"));
        printf("%ld\n", my_getnbr("-42"));
        return 0;
}