C : Create a function to diplay number just with "write" function

How can I write a basic function using just the write function declared in #include <unistd.h>, in order to display a number?

example:

ft_putnbr.c:

int ft_putnbr(int nbr)
{
    write(1, &nbr, sizeof(int));
    return (0);
}

int ft_putchar(char c)
{
    write(1, &c, 1);
    return (0);
}

main.c:

int     ft_putnbr(int nbr);
int     ft_putchar(char c);

int     main(void)
{
    ft_putnbr(6);
    ft_putchar('\n');
    ft_putchar('a');
    return (0);
}

The function ft_putchar works fine, but I would like to do the same with a number, with my ft_putnbr function.

There is no error when I'm compiling or executing the code, but a blank is displayed instead of my number.

i use this one:

void        ft_putnbr(int nbr)
{
    if (nbr < 0)
    {
        ft_putchar('-');
        ft_putnbr(-nbr);
    }
    else if (nbr > 9)
    {
        ft_putnbr(nbr / 10);
        ft_putnbr(nbr % 10);
    }
    else
    {
        ft_putchar(nbr + '0');
    }
}