String Implementation: Member Operators

  String& String::operator = (const String& s)
  {
    if (this != &s)
      {
        if (size_ != s.size_)
          {
            Clear();
            Clone(s);
          }
        else if (size_ != 0) 
          {
            StrCpy (data_, s.data_);
          }
      }
    return *this;
  }

  char& String::operator [] (size_t n)
  // overload of the array access operator
  // Note: [] returns a reference to the element, hence can be used on
  // the left (receiving end) of assignment.
  // Distinctions between [] and Element():
  //    Element(n) returns a value, equal to the element data_[n] 
  //      when 0 <= n < size_ and to '\0' otherwise.
  //    Element(n) cannot be used to assign a (new) value to the element.
  //    [n] returns a reference to the element when 0 <= n < size_
  //      and exits otherwise.
  //    [n] can be used to assign a value to any element except the last.
  {
    if ((size_ == 0) || (n >= size_))
      {
        Error("index out of range");
      }
    return *(data_ + n);
  }