C++ 39.类与对象—多态案例（计算器类）

分别利用普通写法和多态技术实现计算器
多态带来的好处：1.结构组织清晰  2.可读性强  3.对于前期和后期扩展以及维护性高
在实际开发中：对扩展进行开放，对修改进行关闭

#include<iostream>
using namespace std;
#include<string>

//普通写法
class Calculator	//Animal称为虚基类
{
public:
	int getResult(string oper)
	{
		if (oper=="+")
		{
			return m_Num1 + m_Num2;
		}
		else if (oper == "-")
		{
			return m_Num1 - m_Num2;
		}
		else if(oper=="*")
		{
			return m_Num1 - m_Num2;
		}
	}
	int m_Num1, m_Num2;
};


//多态实现计算器
class AbstractCalculator	//Animal称为虚基类
{
public:
	virtual int getResult()
	{
		return 0;
	}
	int m_Num1, m_Num2;
};
//加法
class AddCalculator :public AbstractCalculator
{
public:
	int getResult()
	{
		return m_Num1 + m_Num2;
	}
};
//减法
class SubCalculator :public AbstractCalculator
{
public:
	int getResult()
	{
		return m_Num1 - m_Num2;
	}
};

void test01()
{
	Calculator c;
	c.m_Num1 = 10;
	c.m_Num2 = 10;
	cout << c.m_Num1 << "+" << c.m_Num2 << "=" << c.getResult("+") << endl;
	cout << c.m_Num1 << "-" << c.m_Num2 << "=" << c.getResult("-") << endl;
	cout << c.m_Num1 << "*" << c.m_Num2 << "=" << c.getResult("*") << endl;
}

void test02()
{
	//多态的使用条件：父类的指针或引用指向子类
	AbstractCalculator * abc = new AddCalculator;//父类的指针指向加法对象
	abc->m_Num1 = 1000;
	abc->m_Num2 = 10;
	cout << abc->m_Num1 << "+" << abc->m_Num2 << "=" << abc->getResult() << endl;
	//用完记得销毁，堆取数据手动放入，手动释放
	delete abc;

	//减法运算
	abc = new SubCalculator;//父类的指针指向加法对象
	abc->m_Num1 = 1000;
	abc->m_Num2 = 10;
	cout << abc->m_Num1 << "-" << abc->m_Num2 << "=" << abc->getResult() << endl;
	delete abc;
}
int main()
{
	//test01();
	test02();
	system("pause");
	return 0;
}