CSE 2341 - Honors Principles of Computer Science I

1. CSE 2341 - HonorsPrinciples of Computer Science I Spring 2008 Mark Fontenot mfonten@engr.smu.edu Note Set 8

2. Quick Look Class Diagrams More inheritance

3. Class Diagrams Each student is in 0 or 1 class(es) One or more students in a ClassSection Filled in Diamond: Represents composition

4. Class Diagrams - Inheritance Generalization: Person is a general form of Student and Professor. Student is person Professor is person No real idea of multiplicity in generalization

5. Overriding Member Functions • A member function of a derived class may have the same name and signature of a function in the base class • GradedActivity Class • Need a CurvedActivity class • multiplies the raw score by a curve value before setting the score

6. GradedActivity.h #ifndef GRADEDACTIVITY_H #define GRADEDACTIVITY_H // Grade class declaration class GradedActivity { private: char Letter; float Score; void determineGrade(); public: void SetScore(float S) { Score = S; determineGrade(); } float GetScore() { return Score; } char GetLetter() { return Letter; } }; #endif GradedActivity.h This function will be overridden in the derived class CurvedGrade

7. GradedActivity.h #include “GradedActivity.h" void GradedActivity::determineGrade(void) { if (Score > 89) Letter = 'A'; else if (Score > 79) Letter = 'B'; else if (Score > 69) Letter = 'C'; else if (Score > 59) Letter = 'D'; else Letter = 'F'; } GradedActivity.cpp

8. CurvedActivity.h #ifndef CURVEDACTIVITY_H #define CURVEDACTIVITY_H #include “Grade.h” class CurvedActivity: public GradedActivity{ protected: float rawScore; float percentage;public: // overridden in derived class void setScore (float s) { rawScore = s; // base class setScore method GradedActivity::setScore( rawScore * percentage); } CurvedActivity.h Calls the base class member function

9. CurvedActivity.h void setPercentage (float c) { percentage = c; } float getPercentage() { return percentage; } float getRawScore() { return rawScore; } }; CurvedActivity.h

10. gradeDriver.cpp // main driver#include <iostream>#include “CurvedActivity.h”using namespace std;int main(){ CurvedActivity exam; float numericScore, percentage; cout << “Enter the student’s raw numeric score: “; cin >> numericScore; cout << “enter the curve percentage for this student:”; cin >> percentage; exam.setPercentage (percentage); exam.setScore(numericScore); cout << exam.getRawScore() << exam.getScore() << exam.getLetter(); return 0; } gradeDriver.cpp

11. Overriding Functions • If a derived class overrides a base class member function • objects of the base class call the base class version of the member function • objects of the derived class call the derived class version of the member function

12. Overriding Functions class Base { public: void ShowMsg() { cout << "This is the Base class.\n"; } }; class Derived : public Base { public: void ShowMsg() { cout << "This is the Derived class.\n"; } }; int main(void) { Base B; Derived D; B.ShowMsg(); // ShowMsg of base class called D.ShowMsg(); // ShowMsg of derived class called } This is the Base class. This is the Derived class.

13. Polymorphism Polymorphism - the ability to take many forms Occurs when member functions in a class hierarchy behave differently depending on which object performed the function call Redefinition of a function does not create polymorphism.

14. Polymorphism classBase { public: doCalc(){//something;} calc() { doCalc(); } }; classDerived:public Base { public: doCalc() {//something different;} }; int main() { Derived d; d.calc(); return 0 } Which doCalc() gets called?

15. Binding Times • Static Binding • function call is bound to function implementation at compile time • Dynamic Binding • function call is bound to a function implementation at run-time depending on the type of the object responsible for the call

16. Virtual Function • A virtual function is a function that expects to be redefined in a derived class. • Compiler performs dynamic binding on virtual functions • Declared by placing virtual before the return type in the base class’s function declaration • virtual void myFunction(); • only placed in prototype or header if defined in class