# 13896 - Darray stack for postfix calculation (4/10)
>author: Utin
###### tags: `class`
---

## Brief
See the code below

## Solution 0

#include <iostream>
#include <string>
#include "function.h"
using namespace std;

Darray::~Darray() {
    delete[] data;
}

int& Darray::operator[](int i) {
    return data[i];
}

void Darray::pushback(int x) {
    if (size >= capacity) resize();
    data[size] = x;
    size++;
}

void Darray::popback(void) {
    if (size > 0) size--;
}

void Darray::clear(void) {
    size = 0;
}

int Darray::length(void) {
    return size;
}

int Darray::back(void) {
    return data[size - 1];
}

void Darray::resize(void) {
    capacity *= 2;
    int* tmp = new int[capacity];
    for (int i = 0; i < size; i++) {
        tmp[i] = data[i];
    }
    delete[] data;
    data = tmp;
}

Darray_stack::Darray_stack() : arr() {}

void Darray_stack::operator << (const int& x) {
    arr.pushback(x);
}

void Darray_stack::operator >> (int& x) {
    x = arr.back();
    arr.popback();
}

// Utin

## Reference