Decimal to Hexadecimal

1. Convert decimal to hexadecimal by a recursive function.
2. You may test your function with the following main program.

   
   int main()
   {
       hex(23); cout << endl;
       hex(88); cout << endl;
       hex(127); cout << endl;
       hex(128); cout << endl;
       hex(255); cout << endl;
       hex(256); cout << endl;
       return 0;
   }