lecture7CS32Nachenburg

# lecture7CS32Nachenburg - 1 Wednesday,January27 th...

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1 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]

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2 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?
3 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.

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4 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 . 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
5 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( p ); } float GPA = 1.6; Student s (“David”,19,  GPA ); SayHi( s ); class Student : public Person { public: // new stuff: int getGPA(); private: // new stuff: float m_gpa; Not only can I pass  Person   variables  to that class…

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lecture7CS32Nachenburg - 1 Wednesday,January27 th...

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