DoubleVector

#include <exception>
#include <iostream>
#include <stdexcept>

class Vector {
 public:
  Vector();
  ~Vector();

  double at(unsigned int index) const;
  double operator[](unsigned int index) const { return at(index); }
  unsigned int size() const { return size_; }
  bool empty() const { return size_ == 0u;}
  void push_back(double value);

 private:
  static const unsigned int kInitialSize = 2;

  double* buffer_;
  unsigned int size_;  // Количество хранимых элементов
  unsigned int capacity_;  // Размер буфера

  void increase_buffer();
};

Vector::Vector() :
  buffer_(nullptr),
  size_(0),
  capacity_(0) {
}

Vector::~Vector() {
  delete[] buffer_;
}

double Vector::at(unsigned int index) const {
  if (index >= size_) throw std::out_of_range("No such index");
  return buffer_[index];
}

void Vector::push_back(double value) {
  if (size_ == capacity_) {
    increase_buffer();
  }
  buffer_[size_++] = value;
}

void Vector::increase_buffer() {
  unsigned int new_capacity = capacity_ == 0 ? kInitialSize : 2 * capacity_;
  double* new_buffer = new double[new_capacity];
  for (unsigned int i = 0; i < size_; ++i) {
    new_buffer[i] = buffer_[i];
  }
  delete[] buffer_;
  buffer_ = new_buffer;
  capacity_ = new_capacity;
}

void do_stuff() {
  Vector v;
  v.push_back(4.0);
  v.push_back(5.0);
  v.push_back(3.0);
  v.push_back(2.0);
  v.push_back(1.0);
  for (unsigned int i = 0; i <= v.size(); ++i) {
    std::cout << v[i] << " ";
  }
}

int main() {
  try {
    do_stuff();
  } catch (const std::exception& e) {
    std::cout << "ERROR! " << e.what();
  }
  return 0;
}