do-op alpha

#include <unistd.h>
//////////////////////////
void    ft_putchar(char a)
{
    write(1, &a, 1);
}
/////////////////////////
void    ft_putnbr(int nb)
{
    if ((nb < 0) && (nb != -2147483648))
    {
        nb = -1 * nb;
        if (nb > 9)
        {
            ft_putchar('-');
            ft_putnbr(nb / 10);
            ft_putnbr(nb % 10);
        }
        else
            ft_putchar(nb + '0');
    }
    else if (nb == -2147483648)
    {
        ft_putchar('-');
        ft_putchar('2');
        ft_putnbr(147483648);
    }
    else if (nb > 9)
    {
        ft_putnbr(nb / 10);
        ft_putnbr(nb % 10);
    }
    else
        ft_putchar(nb + '0');
}
//////////////////////////
int     ft_atoi(char *str)
{
    int sign;
    int res;

    sign = 1;
    res = 0;
    while (((*str > 8) && (*str < 14)) || (*str == 32))
        str++;
    if (*str == 45)
    {
        sign = 88;
        str++;
    }
    else if (*str == 43)
        str++;
    while ((*str > 47) && (*str < 58))
    {
        res = (res * 10) + (*str - 48);
        str++;
    }
    if (sign != 1)
    {
        res = -1 * res;
    }
    return (res);
}
//////////////////////////////////////////
int     calculator(int a, int b, char *op)
{
    if (op[0] == 47)
        return (a / b);
    if (op[0] == 37)
        return (a % b);
    if (op[0] == 42)
        return (a * b);
    if (op[0] == 43)
        return (a + b);
    if (op[0] == 45)
        return (a - b);
}
//////////////////////////////
char    *op_checker(char *str)
{
    int run;

    run = 0;
    while (str[run] != '\0')
        ++run;
    if ((run == 1) && ((str[0] == 47) || (str[0] == 37) ||
                (str[0] == 42) || (str[0] == 43) || (str[0] == 45)))
        return (str);
    else
        return ("z");
}
////////////////////////////////
int main(int argc, char **argv)
{
    int run;
    while (argv[run] != '\0')
    {
        ++run;
        if ((run == 4) && (op_checker(argv[2]) != "z"))
            ft_putnbr(calculator(ft_atoi(argv[1]), ft_atoi(argv[3]), argv[2]));
    }
    if ((op_checker(argv[2]) == "z") && (argv[3] != '\0'))
        ft_putnbr(0);
    ft_putchar('\r');
}