Inline Functions, Operator Overloading and Inheritance

COSC 102: Programming in C++

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Outline

• Announcements– Cheating

• Review of Assignment• Inline• Operator Overloading• Lab• Inheritance

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Review of Last Week’s Assignment

• Two weeks ago assignment– bool isLeapYear();– int calcDayOfYear();

• Add it to the Date class

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bool isLeapYear(){if(year%4 == 0 && year % 100 != 0)

return true; else if(year % 400 == 0)

return true; elsereturn false;

}Or{if((year%4 == 0 && year % 100 != 0) || (year %400 ==0)) return true;else return false;}

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int CalcDayOfYear(){int dayCount[12] = {31,28,31,30,31,30,

31,31,30,31,30,31};int dayOfYear = 0;for(int i = 1; i < month; ++i){

dayOfYear += dayCount[i-1];if(i == 2 && isLeapYear() == true) dayOfYear += 1;

}dayOfYear += day;

return dayOfYear;}OR USE SWITCH STATEMENT

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Inline Declaration

Inline functions play an important role in class declarations. When a function is implemented inside a class declaration, it automatically becomes an inline function. This is also known as inline declaration. Why

Speed: function calls are expensive

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Inline Declaration Exampleclass Date{private:

int year;int day;int month;

public: Date();

int getMonth(); int getYear () { return year; }

void setMonth(int m) { month = m;} bool isLeapYear();};

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Inline Functions in Implementation File

There is another way to declare inline functions for classes. You may declare inline functions in the class’s implementation file. For example, to declare function f2 as an inline function, precede the inline keyword in the function header as follows:

// Implement function as inlineinline int Date::getYear(){

return year;}

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Inline Declarations?

Short functions are good candidates for inline functions, but long functions are not.

Space

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Operator Overloading

• Comparing objects == < >• Reading in objects >>• Displaying objects <<

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Overloaded Operators and Objects

• The C++ language provides many symbol operators.

• The C++ operators are designed for specific tasks and data types.

• There are:– relational (<,>,<=,>=,==, !=)– logical (&&, ||, !) – arithmetic (+,–, *, /, %) – increment and decrement (++, – –) – modulus (%)

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• C++ operators (which are just symbols) perform different tasks, depending on how they are used.

• To overload an operator, we must write a specific operator function that is a class member.

• This operator function defines a valid C++ operator that performs the tasks when it is working with an object of that class.

• You may use only valid C++ operators as overloaded operators in classes.

Note: You cannot use characters that are not already operators in C++.OLA/COSC 102

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• The prototype format for an overloaded operator function contains the keyword operator and is followed by the desired operator symbol:

return_type operator symbol(input parameter list);bool operator == (const Date& d);

• The overloaded operators are just regular class functions and follow the same rules.

• When you overload your operators, you have to determine what characteristics makes one object comparable to another object.

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bool Date::operator == (const Date& d){ if (year != d.year) return false; if(month != d.month) return false; if(day != d.day) return false;return true;}bool Date::operator == (const Date& d){if((year==d.year) &&(month ==d.month) &&(day ==d.day)) return true;else return false;}OLA/COSC 102

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Main.cpp

int main(){

Date tobiFemale(1,2,1993);Date mayowaYellow(2,1,1993);if (tobiFemale==mayowaYellow)

cout<<“They are twins”<<endl;else

cout<<“Sowwy”<<endl;}OLA/COSC 102

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Questions

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Human Class Lab

• string name• string color• float size;

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Assignment on Fruit Class

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Inheritance

COSC 102: Programming in C++

Parents and Children

• Imagine having the ability to create a class (a parent class), then derive a new class (a child class) from the parent.

• This child class has the properties and characteristics of the parent.

• The programmer can add additional components unique to the child class.

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Why Is Inheritance So Important? • One reason C++ programmers like the language is

because of the many pre-built classes (vector, string, queue, etc.)

• Many C++ classes have been built, and are intended to be starting points for developers, so that the developer can customize the class as needed.

• REUSABILITY

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Inheritance Basics • The class relationship that models inheritance is

the“is a” relationship.

• The base class, typically, is a general-purpose class.

• The derived class is a special case of the base class.

• The phrase “is a” describes how the classes are related.

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• The format for class inheritance:

class BaseClass{

// members of the base class};

class DerivedClass : access_specifier BaseClass{

// members of the derived class inherit// protected and public members of the // base class

};class CisStudent: public Student{

};

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#include “Date.h”class NaijaDate : public Date{

private:string time;

public:NaijaDate();NaijaDate(int d, int m, int y, string des,

string t);

};

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NaijaDate.cpp

NaijaDate::NaijaDate(){

time = “NaijaTime”;}NaijaDate::NaijaDate(int d, int m, int y, string des, string t): Date(d,m,y,des){

time = t;}OLA/COSC 102 25

Void NaijaDate:: printNDate(){

printDate();cout<<“This is a naija Date”<<endl;cout<<“The time is ”<<time<<endl;

}

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Main.cpp

#include “NaijaDate.h”Int main(){

NaijaDate nd;nd.printDate();nd.getYear();nd.printNDate();

}OLA/COSC 102 27

• This line contains a colon (:) which is C++’s way of saying this BaseClass is the parent for the new DerivedClass.

class DerivedClass : access_specifier BaseClass

• The access specifier, usually the public specifier, dictates access properties for the inherited members.

• Once you have built the new, derived class, you can create derived class objects and use them in the normal fashion.

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Fruit and Banana Class

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Protected Members• There is a third specifier in C++ designed just for

inheritance.

• The protected access specifier provides the programmer greater flexibility when he is working with inherited classes.

• When a class member is specified as protected, that member is inherited by the derived classes, but the member is not accessible outside the base, or derived class.

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The table summarizes the three access specifiers in C++.OLA/COSC 102 31

Access Specifier Specifics and Multiple Inheritance

• There are three access specifiers for classes: private, protected, and public.

• We are familiar with the role these three play when they are used inside a class declaration, such as:

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class C{ private:// members accessible only to class members

protected:// members that are inherited by the child // class// treated as private to the world

public:// members that are inherited by child //class are accessible to the world via an //object of class C

};

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• Another place we use these specifiers is in the first line of a class declaration.

• When used in the first line of a declaration, they are known as base class access specifiers.

• The format is shown below:

class A : public B{

// class info here};

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• The “public B” is the base class access specifier.

• It is possible to create derived classes by using all three of the specifiers: public, protected, and private.

• This base specifier dictates how the base members are treated in the derived classes.

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• The following table summarizes the base class specifiers if class A (below) is used as a base class.

class A{ private: // private members

protected: // protected members

public: // public members

};

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Multiple Inheritance

• It is possible to derive a new class from two or more base classes.

• It is possible to have multiple parents for a child class.

• The syntax for this type of inheritance is shown on the next slide:

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class A class B{ {// base class // base class}; };

class C : public A, public B{// derived class from two base //classes

// class C has both public and //protected members from A and B

};

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• The derived class must have the parent classes in a comma-separated list, and base access specifiers are needed.

• Be sure that the new class does indeed have an is a relationship with both base classes.

• Beginning C++ programmers may believe that using a multiple-base inherited derived class is a time-saving solution for their program.

• In truth, multiple derived classes pose rather complicated design and implementation issues.

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