Stack的模拟实现

栈的特性：后进先出接口一般有：push();   pop();size();empty();top();

#pragma once#include <assert.h>//const size_t N  = 10;//#define NUM 20template<class T>class Stack{public:    Stack()        :_a(NULL)        ,_size(0)        ,_capacity(0)    {}    ~Stack()    {        delete[] _a;        _a = NULL;        _size = _capacity = 0;    }    Stack(const Stack<T>& s);    Stack<T>& operator=(const Stack<T>& s);public:    void Push(const T& x)    {        _CheckCapacity();        _a[_size++] = x;    }    void Pop()    {        assert(_size);        --_size;    }    T& Top()    {        assert(_size > 0);        return _a[_size-1];    }    const T& Top() const    {        assert(_size > 0);        return _a[_size-1];    }    size_t Size()    {        return _size;    }    bool Empty()    {        return _size == 0;    }protected:    void _CheckCapacity()    {        if (_size >= _capacity)        {            size_t newCapacity = _capacity*2 + 3;            T* tmp = new T[newCapacity];            // 类型萃取            if (_a)            {                //memcpy(tmp, _a, _size*sizeof(T));                for (size_t i = 0; i < _size; ++i)                {                    tmp[i] = _a[i];                }            }            _capacity = newCapacity;            delete[] _a;            _a = tmp;        }    }protected:    T* _a;    size_t _size;    //size_t _top;    size_t _capacity;};