Convert Decimal Number to Binary or Hex Without itoa function

Code

#include <stdio.h>
#include <stdint.h>

int dec2binary(uint16_t num, char str[])
{
    int i = 0;
    
    str[0] = '0';
    str[1] = '\0';

    if(!num)
    {
        str[0] = '0';
        str[1] = '\0';
        return 1;
    }
    
    while(num)
    {
        str[i++] = num % 2 + '0';
        num /= 2;
    }
    str[i] = '\0';
    return i;
}

int dec2hex(uint16_t num, char str[])
{
    int i = 0;
    char *literals = "0123456789ABCDEF";

    if(!num)
    {
        str[0] = '0';
        str[1] = '\0';
        return 1;
    }

    while(num)
    {
        str[i++] = literals[num % 16];
        num /= 16;
    }
    str[i] = '\0';
    return i;
}

void print_base(uint16_t num, uint8_t base) {
    char str[20];
    int i;
    int length;
    char tmp;

    if(base == 2)
        length = dec2binary(num, str);
    else 
        length = dec2hex(num, str);

    i = 0;
    length--;

    while(i < length)
    {
        tmp = str[i];
        str[i] = str[length];
        str[length] = tmp;
        i++, length--;
    }

    printf("%s", str);
}

int main() {
    uint16_t num;
    uint8_t base;
    scanf("%hu %hhu", &num, &base);

    print_base(num, base);
    return 0;
}

Solving Approach