C++中为什么要使用多态vs普通写法-案例1

```cpp
#include 
using namespace std;

//分别利用普通写法和多态技术实现计算器

//普通写法
class Calculator
{
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;
		}
		//如果想扩展新的功能，需要修改源码
		//在真是开发中 提倡 开闭原则
		//开闭原则：对扩展进行开放，对修改进行关闭
	}
	int m_Num1;
	int 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;
}
//利用多态实现计算器
//多态的好处：
// 1、组织结构清晰
// 2、可读性强
// 3、对于前期和后期拓展以及维护性高
//实现计算器抽象类
class AbstractCalculator
{
public:
	virtual int getResult() {
		return 0;
	}

	int m_Num1;
	int m_Num2;
};
//加法计算器类
class AddCalculator :public AbstractCalculator
{
public:
	int getResult() {
		return m_Num1 + m_Num2;
	}
};
//减法的计算器类
class SubCalculator :public AbstractCalculator
{
public:
	int getResult() {
		return m_Num1 - m_Num2;
	}
};
//乘法的计算器类
class MulCalculator :public AbstractCalculator
{
public:
	int getResult() {
		return m_Num1 * m_Num2;
	}
};

void test02() {
	//多态使用条件
	//父类指针或者引用指向子类对象

	//加法运算
	AbstractCalculator * abc = new AddCalculator;
	abc->m_Num1 = 10;
	abc->m_Num2 = 10;
	cout << abc->m_Num1 << "+" << abc->m_Num2 << "=" << abc->getResult() << endl;
	//用完后记得销毁
	delete abc;
	//减法运算
	abc = new SubCalculator;
	abc->m_Num1 = 10;
	abc->m_Num2 = 10;
	cout << abc->m_Num1 << "-" << abc->m_Num2 << "=" << abc->getResult() << endl;
	delete abc;
	//乘法运算
	abc = new MulCalculator;
	abc->m_Num1 = 10;
	abc->m_Num2 = 10;
	cout << abc->m_Num1 << "*" << abc->m_Num2 << "=" << abc->getResult() << endl;
	delete abc;

}

int main() {

	//test01();
	test02();

	system("pause");
	return 0;
}