ArrayStack

using System;

public class ArrayStack<T>
{
    private T[] elements;

    public int Count { get; private set; }

    private const int InitialCapacity = 2;

    public ArrayStack(int capacity = InitialCapacity)
    {
        this.elements = new T[capacity];
    }
    public void Push(T element)
    {
        if (this.Count == 0)
        {
            this.elements[this.Count] = element;
            this.Count++;
            return;
        }

        if (this.Count >= this.elements.Length)
        {
            this.Grow();
        }

        var newElements = new T[this.elements.Length];
        this.CopyAllElementsTo(newElements, element);
        this.elements = newElements;
    }

    public T Pop()
    {
        int index = this.Count - 1;
        CheckArrLenght(index);

        T deletedElement = this.elements[index];
        this.elements[index] = default(T);
        this.Count--;

        if (this.Count <= this.elements.Length / 4)
        {
            this.Shrink();
        }
        return deletedElement;
    }

    public T[] ToArray()
    {
        var resultArr = new T[this.Count];
        CopyAllElementsTo(resultArr);
        return resultArr;
    }

    private void Grow()
    {
        var newElements = new T[2 * this.elements.Length];
        Array.Copy(this.elements, newElements, this.Count);
        this.elements = newElements;
    }

    private void CopyAllElementsTo(T[] resultArr)
    {
        for (int i = 0; i < this.Count; i++)
        {
            resultArr[i] = this.elements[i];
        }
    }

    private void CopyAllElementsTo(T[] newElements, T element)
    {
        newElements[0] = element;
        Count++;

        for (int i = 1; i < this.Count; i++)
        {
            newElements[i] = this.elements[i - 1];
        }
    }

    private void CheckArrLenght(int index)
    {
        if (index < 0 || index >= this.Count)
        {
            throw new ArgumentOutOfRangeException();
        }
    }

    private void Shrink()
    {
        T[] newArr = new T[this.elements.Length / 2];
        Array.Copy(this.elements, newArr, this.Count);
        this.elements = newArr;
    }
}