Itoa.c

#include <iostream>
using namespace std;

void reverse(char str[], int length) {
  int start = 0;
  int end = length - 1;
  while (start < end) {
    swap(*(str + start), *(str + end));
    start++;
    end--;
  }
}

char *itoa(int num, char *str, int base) {
  int i = 0;
  bool isNegative = false;

  if (num == 0) {
    str[i++] = '0';
    str[i] = '\0';
    return str;
  }

  if (num < 0 && base == 10) {
    isNegative = true;
    num = -num;
  }

  while (num != 0) {
    int rem = num % base;
    str[i++] = (rem > 9) ? (rem - 10) + 'a' : rem + '0';
    num = num / base;
  }

  if (isNegative)
    str[i++] = '-';

  str[i] = '\0';

  reverse(str, i);

  return str;
}

int main() {
  char str[100];
  cout << "Base:10 " << itoa(1567, str, 10) << endl;
  cout << "Base:10 " << itoa(-1567, str, 10) << endl;
  cout << "Base:2 " << itoa(1567, str, 2) << endl;
  cout << "Base:8 " << itoa(1567, str, 8) << endl;
  cout << "Base:16 " << itoa(1567, str, 16) << endl;
  return 0;
}