Stack.cs

public class Stack<T>
{
    private readonly T[] _stack;
    private readonly int _size;
    private int _topMostItemIndex = -1;

    public Stack(int size = 16)
    {
        _size = size;
        _stack = new T[size];
    }

    public bool IsEmpty => _topMostItemIndex == -1;
    private bool IsFull => _size == _topMostItemIndex + 1;

    public void Push(T value)
    {
        if (IsFull)
        {
            throw new Exception("Stack is full");
        }

        _stack[++_topMostItemIndex] = value;
    }

    public T Pop()
    {
        if (IsEmpty)
        {
            throw new Exception("Stack is empty");
        }

        return _stack[_topMostItemIndex--];
    }

    public T Peek()
    {
        if (IsEmpty)
        {
            throw new Exception("Stack is empty");
        }

        return _stack[_topMostItemIndex];
    }
}