Convert int to String or char* yourself

It was asked by an interviewer to me in an interview and I found a bit of equivalent code in

http://www.strudel.org.uk/itoa/

char* version 

char* itoa(int value, char* result, int base) {

  // check that the base if valid

  if (base < 2 || base > 36) { *result = '\0'; return result; }

  char* ptr = result, *ptr1 = result, tmp_char;

  int tmp_value;

  do {

   tmp_value = value;

   value /= base;

   *ptr++ = "zyxwvutsrqponmlkjihgfedcba9876543210123456789abcdefghijklmnopqrstuvwxyz" [35 + (tmp_value - value * base)];

  } while ( value );

  // Apply negative sign

  if (tmp_value < 0) *ptr++ = '-';

  *ptr-- = '\0';

  while(ptr1 < ptr) {

   tmp_char = *ptr;

   *ptr--= *ptr1;

   *ptr1++ = tmp_char;

  }

  return result;

 }

std::string version

std::string itoa(int value, int base) {

  std::string buf;

  // check that the base if valid

  if (base < 2 || base > 16) return buf;

  enum { kMaxDigits = 35 };

  buf.reserve( kMaxDigits ); // Pre-allocate enough space.

  int quotient = value;

  // Translating number to string with base:

  do {

   buf += "0123456789abcdef"[ std::abs( quotient % base ) ];

   quotient /= base;

  } while ( quotient );

  // Append the negative sign

  if ( value < 0) buf += '-';

  std::reverse( buf.begin(), buf.end() );

  return buf;

 }