C++多态、纯虚函数和利用多态写计算器

#include
#include
using namespace std;
//多态（动态多态->派生类和虚函数）
//条件：有继承关系，子类重写父类虚函数（virtual）
class an {
public:
	virtual void shuohua() {//虚函数
		cout << "动物会说话：" << endl;
	}
};
class cat : public an {
public:
	void shuohua() {
		cout << "喵喵喵" << endl;
	}
};
class dog : public an {
public:
	 void shuohua() {
		cout << "汪汪汪" << endl;
	}
};
//void shuo(an& ann)【地址早绑定 编译阶段就确定了函数地址】
void shuo(an& ann) {//父类引用或指针
	ann.shuohua();
}

int main() {
	an a;
	shuo(a);
	cat ca;
	shuo(ca);
	dog doo;
	shuo(doo);
}

创建父类并用父类创建子类对象

		jisuanji* ab;//创建父类
	case '+' : ab = new jiafa;//用父类指针创建子类对象

#include
#include
using namespace std;
//多态实现计算器
//对拓展进行开放，对修改进行关闭
class jisuanji {
public:
	virtual int get() {
		return 0;
	}
	int num_1, num_2;
};
class jiafa : public jisuanji {
public:
	int get() {
		return num_1 + num_2;
	}
};
class jianfa : public jisuanji {
public:
	int get() {
		return num_1 - num_2;
	}
};
class chengfa : public jisuanji {
public:
	int get() {
		return num_1 * num_2;
	}
};
class chufa : public jisuanji {
public:
	int get() {
		return num_1 / num_2;
	}
};
void ceshi() {
	cout << "input type:(+.-.*./):" << endl;
	char leixing;
	cin >> leixing;
	switch (leixing)
	{
		jisuanji* ab;//创建父类
	case '+' : ab = new jiafa;//用父类指针创建子类对象
		cin >> ab->num_1;
		cin >> ab->num_2;
		cout << ab->num_1 << "+" << ab->num_2 << "=" << ab->get () << endl;
		delete ab;
		//new的数据要delete销毁（不销毁os也会销毁）
		break;
	case '-':ab = new jianfa;
		cin >> ab->num_1;
		cin >> ab->num_2;
		cout << ab->num_1 << "-" << ab->num_2 << "=" << ab->get() << endl;
		delete ab;
		break;
	case '*':ab = new chengfa;
		cin >> ab->num_1;
		cin >> ab->num_2;
		cout << ab->num_1 << "*" << ab->num_2 << "=" << ab->get() << endl;
		delete ab;
		break;
	case '/':ab = new chufa;
		cin >> ab->num_1;
		cin >> ab->num_2;
		cout << ab->num_1 << "/" << ab->num_2 << "=" << ab->get() << endl;
		delete ab;
		break;
	}
}
int main() {
	ceshi();
	ceshi();
	ceshi();
	ceshi();
}

//纯虚函数(有一个就是抽象类)
virtual void shuohua() = 0;
//无法实例化对象-> an a|new an会报错
//抽象类的子类必须重写父类的纯虚函数（否则子类不能实例化对象）

#include
#include
using namespace std;
//纯虚函数->抽象类
class an {
public:
	//纯虚函数(有一个就是抽象类)
	virtual void shuohua() = 0;
	//无法实例化对象->	an a|new an会报错
	//抽象类的子类必须重写父类的纯虚函数（否则子类不能实例化对象）

};
class cat : public an {
public:
	void shuohua() {//必须重新纯虚函数
		cout << "喵喵喵" << endl;
	}
};
class dog : public an {
public:
	void shuohua() {
		cout << "汪汪汪" << endl;
	}
};

void shuo(an& ann) {//父类引用或指针
	ann.shuohua();
}

int main() {
	cat ca;
	shuo(ca);
	dog doo;
	shuo(doo);
}