开闭原则
对扩展开放，对修改关闭，类的改动是通过增加代码进行的，而不是修改源代码 如下所示，如果想要扩展乘法、除法、取模等算法，就不用修改原码，只需增加新类 class AbstractCalculator{ public: virtual void setOperatorNum(int a, int b) = 0; virtual int getResult() = 0; }; class PlusCalculator:public AbstractCalculator{ public: void setOperatorNum(int a, int b)override{ m_a = a; m_b = b; } int getResult()override{ return m_a + m_b; } private: int m_a{0}; int m_b{0}; }; class MinusCalculator:public AbstractCalculator{ public: void setOperatorNum(int a, int b)override{ m_a = a; m_b = b; } int getResult()override{ return m_a - m_b; } private: int m_a{0}; int m_b{0}; }; int main() { AbstractCalculator* calculator = new PlusCalculator; calculator->setOperatorNum(10, 20); cout << calculator->getResult() << endl; delete calculator; calculator = nullptr; calculator = new MinusCalculator; calculator->setOperatorNum(10, 20); cout << calculator->getResult() << endl; delete calculator; calculator = nullptr; return 0; }