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lecture7 - Wednesday January 27 th • Polymorphism •...

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Unformatted text preview: Wednesday, January 27 th • Polymorphism • Virtual Functions • Virtual Destructors • Pure Virtual Functions Office hours on Wed, Feb 3 rd will be from 9-10am Carey will be attending the Society of Women Engineers Luncheon from 12-1pm on Wed, Feb 3 rd Everyone’s invited to join me for lunch (first come, first served) Contact Ashley Jin for more details: [email protected] Polymorphism Consider a function that accepts a Person as an argument void LemonadeStand( Person &p ) { cout << “Hello “ << p .getName(); cout << “How many cups of ”; cout << “lemonade do you want?”; } Can we also pass a Student as a parameter to it? void main(void) { Person p; LemonadeStand(p); } We know we can do this: void main(void) { Student s; LemonadeStand(s); } But can we do this? Polymorphism Consider a function that accepts a Person as an argument void LemonadeStand( Person &p ) { cout << “Hello “ << p .getName(); cout << “How many cups of ”; cout << “lemonade do you want?”; } Can we also pass a Student as a parameter to it? Person I’d like to buy some lemonade. We only serve people. Are you a person? Yes. I’m a person. I have a name and everything. class Person { public: string getName (void); ... private: string m_sName; int m_nAge; }; Ok. How many cups of lemonade would you like? Mom. I think that’s Lucy Lu! Shhhh. Student Polymorphism Consider a function that accepts a Person as an argument void LemonadeStand( Person &p ) { cout << “Hello “ << p .getName(); cout << “How many cups of ”; cout << “lemonade do you want?”; } Can we also pass a Student as a parameter to it? I’d like to buy some lemonade. We only serve people. Are you a person? Prove it to us! class Student : public Person { public: // new stuff: int getStudentID(); private: // new stuff: int m_nStudentID; }; Hmm. I’m a student but as far as I know, all students are people! Well, you can see by my class declaration that all students are just a more specific sub-class of people . public Person But do you have a name like a person? Since I’m based on a Person , I have every-thing a Person has… Including a name! Look! class Person { public: string getName (void); ... private: string m_sName; int m_nAge; Well, as long as you’re a person, we can serve you. Mom. It’s a NERD!!! Uh huh. getName class Person { public: string getName(void) { return m_name; } ... private: string m_name; int m_age; }; Polymorphism The idea behind polymorphism is that once I define a function that accepts a (reference or pointer to a) Person … void SayHi( Person &p ) { cout << “Hello “ << p.getName(); } main() { Person p (“Eric”,18); SayHi(...
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lecture7 - Wednesday January 27 th • Polymorphism •...

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