converts integers to string.

itoa.c

int power(int n, int pow) {
    int res = n;
    if (pow == 0) return 1;
    while (--pow > 0) res *= n;
    return res;
}

// increases 'pow' until find the smallest power of 10
// which is bigger than the number. and its gives the digit count.
int count_digits(int nbr) {
    if (nbr == 0) return 1; //zero is smaller than all powers of ten.
    if (nbr < 0) nbr = -nbr; //get absolute value
    int pow = 0;
    while (nbr >= power(10, pow++));
    return pow - 1;
}

//if you divide 12345(nbr) by 100(power(10, digit - 1)), it would be equal to 123(nbr / power(10, digit - 1)).
//if you continue, and you divide it by 10, its remainder will be 3((nbr / power(10, digit - 1)) % 10).
int get_digit(int nbr, int digit) {
    if (nbr < 0) nbr = -nbr;
    return (nbr / power(10, digit - 1)) % 10;
}

char *ft_itoa(int nbr) {
    int negativity = nbr < 0; //negative numbers are '-' signed, so you have to care it.
    int digit_amount = count_digits(nbr);
    int length = digit_amount + negativity;
    char *result = malloc( (length));

    if (negativity) result[0] = '-';

    int i = negativity; //if positive, start at 0. index, otherwise start at 1. index because we have '-' sign.
    while (i < length) {
        result[(length - 1) - i + negativity] = get_digit(nbr, i + 1 - negativity) + 48;
        i++;
    }

    return result;
}

int main() {
    printf("numb: %s", ft_itoa(-12948));
}