#include <iostream>
#include <cmath>

 char *itoa (int);

 char *
 itoa (int i)
 {
   char *ret = 0;
   ret = new char[11];

   int anfang_l = std::log10 (i);
   while (int l = std::log10 (i))
     {
       int div = std::pow (10, l);
       int ziffer = i / div;
       ret[anfang_l - l] = ziffer + '0';
       i -= div * ziffer;
     }
   ret[anfang_l] = i + '0';
   ret[anfang_l + 1] = '\0';

   return ret;
 }

 int
 main ()
 {
   std::cout << itoa (12345) << '\n';
 }