Car. Sedan Truck Pickup SUV

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1 Lecture #7 Introduction Inheritance, Composition, and Polymorphism In terms of object-oriented programming, inheritance is the ability that enables new classes to use the properties and methods of existing classes through the declaration of inheritance. For example, the word car is a general term that can describe many kinds of vehicles including sedan, truck, pickup, SUV, and more. All these vehicles are specialized cars. A car must have an engine, tires, and a driver s seat no matter what kind of car it is. Therefore, if a sedan is a kind of car, then a sedan must have an engine, tires, and a driver s seat. Car Sedan Truck Pickup SUV Fig 1 Inheritance is the act that applies the properties and methods of the Car class to the Sedan class; thus, an instance of Sedan can use members of Car without the need to re-define these Car members in Sedan. A class that is inherited by other classes is called a base class (or parent class). The class that does the inheriting is called a derived class (or child class). In a sense, a derived class is a specialized subset of a base class. Polymorphism is the concept that allows multiple forms of a given method to exist in a class, each of the form is designed for handling a special situation. Polymorphism also allows a child class to override the definition of methods of the parent class. C++ inheritance In C++, programmers create a child class (officially known as derived class ) with the following syntax to declare the inheritance from a parent class (aka base class ), where AccessSpecifier is public, private, or protected. By the way, if no AccessModifier is given, private is the default. class childclassname: AccessModifier parentclassname childclass members; ; The following illustrates how to declare a new class named Cellphone as child (derived) class of an existing class named Telpehone. It is necessary to note that the Telephone class which is the parent (based) class must be declared before the child can be declared. class cellphone: public Telephone After the declaration, the child class can inherit all of the shared members of the base class and create its own menbers. In other words, inheritance is for a child class to gain access to all the public or protected members (such as properties and methods) of the parent class, and use them like its own members. Both public and protected members of a parent class are shareable members to the child class, while private members are not shareable. A later section will discuss how these access modifier work in inheritance. The advantage of inheritance in object-oriented programming is the sharing of codes. In a given program, you only have to define what a car is ONCE by creating a Car class. All the specialized cars, such as sedan, truck, pickup, and SUV, can reference to the Car class Visual C++ Programming Penn Wu, PhD 178

2 and share the codes defined in the Car class. It is just like saying a sedan is a car, a truck is a car, and a pickup is a car without the need to define what a car is over and over again. Class inheritance The following is a class named Car containing two public instance variables: mpg and tanksize. It also has a protected method named mileage() to calculate the mileage, and a private variable named securitycode. The instructor creates this Car class to be inherited by others. ref class Car // base class // open to the entire program int mpg; int tanksize; protected: int mileage() return mpg * tanksize; private: // not open to child class int securitycode; ; The following is an example that create the Sedan class as child to the Car class. The Sedan class also has two public variables of int type: tirenumber and ml. The default constructor, Sedan(), defines all the default values of the Sedan class. All the shareable members of the Car class, mpg, tanksize, and mileage(), are used by the Sedan as its own members. In the words, Sedan inherits all sharable members of Car. Shareable members of Car are also members of the Sedan class. ref class Sedan : public Car // declare Sedan a child of Car int tirenumber; int ml; Sedan() tirenumber = 4; mpg = 34; tanksize = 16; ml = mileage(); ; The declaration on inheritance forces the Car class to share all the public properties and public methods with the Sedan class. Programmers do not need to declare variables mpg and tanksize and the mileage() method again when they create the Sedan class. In other words, the Sedan class inherits all the public members of the Car class. A child class, even as a child, is still an individual class. The way to declare, create, or add members of a child class is exactly the same as that of any C++ class. In the following example, the instructor adds a public method named TurboIt(). Visual C++ Programming Penn Wu, PhD 179

3 ref class Sedan : public Car // declare Sedan a child of Car int tirenumber; int ml; Sedan() tirenumber = 4; mpg = 34; tanksize = 16; ml = mileage(); void TurboIt() mpg = mpg * 1.5; ; Some programmers prefer declaring a class method inside the class body, and then use the scope resolution operator (::) to define details of the member method outside the class body, as illustrated below. The scope resolution operator (::), which, in C++, can be used to define the already declared member functions. ref class Sedan : public Car // declare Sedan a child of Car int tirenumber; int ml; Sedan() tirenumber = 4; mpg = 34; tanksize = 16; ml = mileage(); void TurboIt(); ; void Sedan::TurboIt() mpg = mpg * 1.5; To use members in both base (parent) and derived (child) classes, you can create an instance of Sedan in the main() method, such as s1 in the following code. You can certainly create an instance of Car (s2). Interestingly, you can also declare an object as Car (such as s3 ), but create the object as Sedan. Sedan^ s1 = gcnew Sedan; Car^ s2 = gcnew Car; Car^ s3 = gcnew Sedan; Visual C++ Programming Penn Wu, PhD 180

4 The s1 object is instantiated as Sedan, s2 object is instantiated as a Car, and s3 is declared as Car but is instantiated as Sedan. The difference between s1 and s3 is that s1 can uses all shared members of the Car class through inheritance and every member of the Sedan class, while s3 can use all shared members of Car and the default values defined in the Sedan() constructor. Instance of the Car class can only use any member of the Car class, and cannot access the Sedan() default constructor. Object Car Sedan mpg tanksize mileage() securitycode tirenumber() ml Sedan() s1 yes yes yes no yes yes yes s2 yes yes yes no no no no s3 yes yes yes no no no yes Once Sedan is declared as a derived class (the child class) of the Car class, you can directly use properties and methods of the Car class with the member-of (->) operator. Technically, all the public members in the Car class are treated as members of the Sedan class. For example, to the use mpg property of the Car class from a Sedan object, use: s1->mpg To assign a value to the mpg property, use: s1->mpg = 72; Similarly, to use a method of the Car class, use: s1->mileage(); The following is the complete code. ref class Car // base class // open to the entire program int mpg; int tanksize; protected: int mileage() return mpg * tanksize; private: // not open to child class int securitycode; ; ref class Sedan : public Car // declare Sedan a child of Car int tirenumber; int ml; Sedan() Visual C++ Programming Penn Wu, PhD 181

5 tirenumber = 4; mpg = 34; tanksize = 16; ml = mileage(); void TurboIt() mpg = mpg * 1.5; ; String^ str = "Car\tMPG\tTank Size\tTires\tMileage\n"; Sedan^ s1 = gcnew Sedan; // instance of Sedan s1->turboit(); // member of Sedan only str += "s1\t" + s1->mpg + "\t" + s1->tanksize + "\t"; str += s1->tirenumber + "\t" + s1->ml + "\n"; Car^ s2 = gcnew Car; str += "s2\t" + s2->mpg + "\t" + s2->tanksize + "\n"; Car^ s3 = gcnew Sedan; str += "s3\t" + s3->mpg + "\t" + s3->tanksize + "\t"; //str += s3->tirenumber + "\t" + s3->ml + "\n"; MessageBox::Show(str); The output looks: Access modifiers Choosing a proper Access modifier can make a big difference in inheritance. The private members of a base class are private to the base class only; therefore, the derived class cannot access them. The protected members can be inherited by the derived class; however, the derived class cannot modify values or content of a protected member of the base class. The public members of a base class can be inherited either as public members or as private members by the derived class. In other words, the public members of the base class can become either public or private members of the derived class. The protected Access modifier is similar to private. Its only difference occurs in fact with inheritance. The following table summarizes the different access types according to who can access them in the following way: Access public protected private members of the same class Yes Yes Yes members of derived classes Yes Yes No not members Yes No No Visual C++ Programming Penn Wu, PhD 182

6 In the following example, the instructor declares three instance variables: category, IsRegistered, and origin. They are specified as public, private, and protected respectively. The Car class has a default constructor, Car(), which specifies the default values of IsRegistered and origin. ref class Car // base class String^ category; private: Boolean IsRegistered; protected: String^ origin; Car() IsRegistered = true; origin = "Nakano Japan"; ; The following is a derived class that has only a default constructor, Sedan(), to specify what an instance of the Sedan class should do. It is necessary to note that category is a public member of the Car ; therefore, Sedan can use it and modify its value. Interestingly, origin is a protected member, yet Sedan can still modify its value. This is because Sedan inherits origin from Car which makes origin a member of Sedan. ref class Sedan : public Car Sedan() category = "4 door Sedan"; origin = "Dayton, OH, USA"; MessageBox::Show(category + "\n" + origin); ; In the following example, the instructor attempts to modify the value of orgin inside the main() method. This is an illegal act because the main() method is neither a member of the Sedan class nor a member of the Car class. Sedan s1; s1.origin = "Jechiu, Korea"; The compiler will return the following error message: error C2248: 'Car::origin' : cannot access protected member declared in class 'Car' 1.cpp(13) : see declaration of 'Car::origin' 1.cpp(8) : see declaration of 'Car' Apparently a child class (derived class) can access and modify value or contents of both public and protected members. The following code attempts to access the private member of Car class from the child class. ref class Sedan : public Car Visual C++ Programming Penn Wu, PhD 183

7 Sedan() category = "4 door Sedan"; origin = "Dayton, OH, USA"; IsRegistered = false; MessageBox::Show(category + "\n" + origin); ; The attempt is illegal and the compile will return the following error message: error C2248: 'Car::IsRegistered' : cannot access private member declared in class 'Car' 1.cpp(11) : see declaration of 'Car::IsRegistered' 1.cpp(4) : see declaration of 'Car' The following is the complete code for you to test. ref class Car // base class String^ category; private: Boolean IsRegistered; protected: String^ origin; Car() IsRegistered = true; origin = "Nakano Japan"; ; ref class Sedan : public Car Sedan() category = "4 door Sedan"; origin = "Dayton, OH, USA"; MessageBox::Show(category + "\n" + origin); ; Sedan s1; Default constructor of the parent class is executed by default when inheritance occurs. In the following example, the GetFoot class is the parent class and the GetInch is the child class. By creating an instance of the GetInch class, the default constructor of both classes must execute. The sequence of execution is: parent first, child second. Visual C++ Programming Penn Wu, PhD 184

8 #include "InputBox.cpp" ref class GetFoot protected: int feet; GetFoot() // defaut constructor feet = Convert::ToInt32(InputBox::Show("Enter the feet:")); ; ref class GetInch : GetFoot protected: int inch; int height; GetInch() // default constructor inch = Convert::ToInt32(InputBox::Show("Enter the inch:")); height = feet * 12 + inch; ; String^ str = ""; GetInch^ g1 = gcnew GetInch; // call GetFoot() and GetInch() MessageBox::Show("You are " + g1->height + " inches tall."); return 0; A parent class can share its members with two or more child classes. The following is an example of a supportive class named Socal which is create to provide shared members; therefore, it is a based class. ref class Socal // base class protected: int staff, faculty; void setvalues(int x, int y) staff=x; faculty=y; int total() Visual C++ Programming Penn Wu, PhD 185

9 return (staff + faculty); ; In the Socal (Southern California) area, there are three campuses: Pomona, Long Beach, and Sherman Oaks. Figure 2 explains the relationships among the classes. Socal Pomona Long Beach Sherman Oaks Figure 2 The child classes can inherit and use the shared members of the Socal (parent) class. Noticeably inheritance is a one-way relationship and only the child class can inherit the parent class. The following is a dummy (aka. empty ) which inherits every from the Socal class. ref class ShermanOaks : public Socal ; // an empty class In the following code, the Pomona class inherits the Socal class, yet it modify the public method named total(). ref class Pomona: public Socal // derived class int total() return (staff * faculty * 0.6); ; The Long Beach class can manipulate members of the Socal class in another way (assuming half of the faculties in Long Beach also teach at Pomona, so the formula is different): ref class LongBeach: public Socal // derived class int total() return (staff + faculty / 2); ; The following is the complete code that illustrates the concept. ref class Socal // base class protected: int staff, faculty; void setvalues(int x, int y) Visual C++ Programming Penn Wu, PhD 186

10 staff=x; faculty=y; int total() return (staff + faculty); ; ref class ShermanOaks : public Socal ; // an empty class ref class Pomona: public Socal // derived class int total() return (staff * faculty * 0.6); ; ref class LongBeach: public Socal // derived class int total() return (staff + faculty / 2); ; Pomona^ s1 = gcnew Pomona(); s1->setvalues(15, 7); LongBeach^ s2 = gcnew LongBeach(); s2->setvalues(12, 6); ShermanOaks^ s3 = gcnew ShermanOaks(); s3->setvalues(10, 4); String^ str = "Total employees:\n"; str += s1->total() + "\n" + s2->total() + "\n" + s3->total(); MessageBox::Show(str); return 0; The output looks: Multiple layer inheritance A derived (child) class can be a base (parent) class to its own derived class. For example, a variable x is defined in mybase class. The Square class inherits x from mybase and passes it on Visual C++ Programming Penn Wu, PhD 187

11 to the Cube class. The Square class has a function named calsquare(), which will also be used by the Cube class. MyBase (parent class) Square (child class) Cube (grandchild class) To demonstrate how such a three-layer inheritance works, create the mybase class with a variable x as shown below: ref class mybase double x; ; Create the Square class as a derived class of the mybase class, and then define the calsquare() function as a public member of the Square class. So, the mybase class cannot use this calsquare() function. ref class Square : public mybase int calsquare() // calculate square of x return x * x; ; Create the Cube class as a derived class of the Square class. Technically it is the grandchild of the mybase class. Also, create the calcube() function as the member of the Cube(), so neither Square class nor mybase class can use it. ref class Cube : public Square int calcube() // calculate cube of x return calsquare() * x; ; Finally, in the main() function initiate a Cube object named myno, which will use the x variable (inherited from the mybase class by way of the Square class) and the calsquare() function (inherited from the Square class). ref class mybase double x; ; ref class Square : public mybase int calsquare() // calculate square of x Visual C++ Programming Penn Wu, PhD 188

12 return x * x; ; ref class Cube : public Square int calcube() // calculate cube of x return calsquare() * x; ; Cube^ c1 = gcnew Cube(); c1->x = 3; String^ str = c1->x + "\n"; // inherit x from mybase str += c1->calsquare() + "\n"; // inherit from Square str += c1->calcube() + "\n"; MessageBox::Show(str); return 0; The calcube() function is a member of the Cube class. No inheritance applies to it. The following is another demonstration of how multiple layer inheritance works. The instructor creates three classes. Their relationship is illustrated by the following figure. TicketPrice (parent class) DiscountPrice (child class) InvoicePrice (grandchild class) The functionality of each class is described below: TicketPrice: Ask user to enter the ticket price (or price on a tag), and then set the sale price equal to the unit price. DiscountPrice: Ask user to enter the discount rate and then calculate the sale price. InvoicePrice: Ask user to enter the tax rate, calculate the final price, and rount the value. Based on the above description, the instructor wrote the following code to create the TicketPrice class. ref class TicketPrice // parent double unitprice; double saleprice; TicketPrice() // default constructor unitprice = Convert::ToDouble(InputBox::Show("Unit price: ")); saleprice = unitprice; ; The following is the code for the DiscountPrice. This class inherits both unitprice and saleprice members from the TicketPrice class. It also creates its own member dicsountrate. Visual C++ Programming Penn Wu, PhD 189

13 ref class DiscountPrice : TicketPrice // child double discountrate; DiscountPrice() // default constructor discountrate = Convert::ToDouble(InputBox::Show("Discount rate (%): ")) * 0.01; saleprice = unitprice * (1- discountrate); ; The following is the code for InvoicePrice class. This class inherits both unitprice and saleprice members from the TicketPrice class. It also inherits dicsountrate from the DiscountPrice class. Additionally, it adds two members RoundIt() and taxtrate. ref class InvoicePrice : DiscountPrice // grandchild private: double roundit(double n) return Math::Round(n, 2); protected: double taxrate; double finalprice; InvoicePrice() // default constructor taxrate = Convert::ToDouble(InputBox::Show("Tax rate (%): ")) * 0.01; finalprice = saleprice * (1 + taxrate); finalprice = roundit(finalprice); ; Composition In terms of object-oriented, composition is the creation of a new class which contains instance of other existing classes. The following figure illustrates how a Student class consists of an instance of Name class, an instance of Address class, and an instance of Major class. In other words, every student has a name, an address, and a major. Name n1 Student Address a1 Major m1 The following uses four code snippets to illustrate the concept. ref class Name Ref class Address ref class Major ref class Student Private: Name^ n1; Address^ a1; Major^ m1; Visual C++ Programming Penn Wu, PhD 190

14 The term composition can be further divided into two categories of relationship: composition and aggregation. If an object is exclusively owned by another object, they are in the composition relationship. If an object can be shared by two or more objects, they are in the aggregation relationship. In the above example, each Student must have one and only one Name object; therefore, a Student has a name is a composition relationship. Since two or more students could live in the same house; an address could be shared by two or more student. Student and Address are in an aggregation relationship. The following is a sample code that demonstrates how composition works. ref class Name String^ get() return "object of Name."; ; ref class Address String^ get() return "object of Address."; ; ref class Major String^ get() return "object of Name."; ; ref class Student String^ report; private: Name^ n1 = gcnew Name(); Address^ a1 = gcnew Address(); Major^ m1 = gcnew Major(); Student() report = n1->get() + "\n" + a1->get() + "\n" + m1->get(); ; Student^ s1 = gcnew Student(); MessageBox::Show(s1->report); A sample output looks: Visual C++ Programming Penn Wu, PhD 191

15 In the following example, composition occurs because each Car object must have an Engine object. The instructor, however, purposely creates an instance of Engine inside the default constructor of the Car class. ref class Engine bool IsGasIn; String^ status; Engine() IsGasIn = true; status = "Engine started."; ; ref class Car String^ report; Car() Engine^ e1 = gcnew Engine(); report = e1->status + "\nhas gas: " + e1->isgasin; ; Car^ c1 = gcnew Car(); MessageBox::Show(c1->report); Polymorphism Polymorphism is a biological term that literally means many forms or shapes. The objectoriented paradgin support two major types of polymorphism: method (or function) polymorphism and subclass polymorphism. In terms of programming, method (or function) polymorphism is the ability to allow multiple methods of a given class share the same identifier (name) but behave differently. When building an application for calculating the body mass index (BMI) programmers frequently have to allow a method to behave in serveral ways. BMI is a measure of relative weight based on an individual's mass and height. The following is the formulas used in the U.S. for calculating BMI, where w is the body weight in pounds (lb) and h is the height in inches. BMI = (w /h 2 ) 703 Visual C++ Programming Penn Wu, PhD 192

16 In the following example, the instructor creates two forms of the getbmi() method for the BMI class. Each form takes different types of parameters and return values of different type, yet all the two forms have exactly the same identifier getbmi. This an example of method polymorphism. Some textbook refers this kind of polymorphism as overloading. Overloading happens when you define two or more forms of methods with the same identifier in the same class. ref class BMI double getbmi(double w, double h) // form 1 return (w / (h*h)) * 703; String^ getbmi(int w, int h) //form 2 return ( ((double) w / (h*h)) * 703 ) + ""; ; String^ str = ""; BMI^ b1 = gcnew BMI; str += b1->getbmi(92.7, 1.74) + "\n"; // form 1 str += b1->getbmi(185, 66) + "\n"; // form 2 MessageBox::Show(str); return 0; Polymorphism can happen among functions that do not belong to any class. The following code contains two forms of getf() function. They both use the formula C = (5/9) (F - 32) to convert Fahrenheit to Celsius; however, they take different types of parameter and return values of different types. This example illustrates function polymorphism. double getf(double f) // form 1 return ((double) 5/ (double) 9) * (f - 32); float getf(string^ f) // form 2 return ((double) 5/ (double) 9) * (Convert::ToDouble(f) - 32); Visual C++ Programming Penn Wu, PhD 193

17 String^ str = ""; str += getf(92.7) + "\n"; // form 1 str += getf("92.7") + "\n"; // form 2 MessageBox::Show(str); return 0; Polymorphism can happen between a method of parent class and its child class. Subclass polymorphism is also known as overriding. Overrding happens when you redefine a method inherited from a parent class. There are in fact, two formulas for calculating BMI, as shown in the following table. Metric system BMI = w /h 2 where w is the body weight in kilograms (kg) and h is the height in meters (m). U.S. system BMI = (w /h 2 ) 703 where w is the body weight in pounds (lb) and h is the height in inches. Most countries adapt the metric system. The United States is one of the very few countries that have not yet adapted the metric system; therefore, it is reasonable to treat the U.S. as an exception. In the following code, the instructor creates a paranet class named BMI with a getbmi() method that uses the metric-system formual to return BMI values. The instructor also create a child class named USBMI which inherits public getbmi method from the BMI class. The subclass polymorphism happens when the USBMI class override the getbmi() method. ref class BMI double getbmi(double w, double h) // form 1 return w/(h*h); ; ref class USBMI : BMI double getbmi(double w, double h) // form 2 return (w/(h*h)) * 703; // overriding ; String^ str = ""; BMI^ b1 = gcnew BMI; USBMI^ u1 = gcnew USBMI; str += b1->getbmi(90.3, 1.76) + "\n"; // form 1 str += u1->getbmi(191.6, 66.5) + "\n"; // form 2 MessageBox::Show(str); Visual C++ Programming Penn Wu, PhD 194

18 return 0; The getbmi() method in both BMI and USBMI classes have the same identifier, they take the same types of paremeters, and they return the same type of values. However, they use different formula to calculate the BMI values. Review Question 1. The following is an example of. ref class Blue : public Color A. inheritance. B. encapsulation. C. data hiding. D. abstract data types. 2. Given the following code segment, which statement is correct? ref class Sedan: public Car A. Sedan is a base class B. Car is a derived class C. The Sedan class is a subclass to the Car class. D. The Car class is a subclass to the Sedan class. 3. Given the following code segment,. ref class Apple: public Orange... A. Orange is the derived class B. Orange is the associated class C. Apple is the derived class D. Apple is the base class 4. Given the following code segment,. ref class Apple: public Orange... A. Orange inherits shareable properties and methods from Apple. B. Apple inherits shareable properties and methods from Orange. C. Apple is a derived class, so it cannot add its own class members. D. Apple defines data and features for Orange. 5. Given the following code, which member of the Apple class cannot be accessed by the Orange class. ref class Apple private: double stockprice; protected: double dividend; double shares; ; ref class Orange: public Apple A. stockprice and dividend B. dividend and share C. shares and stockprice Visual C++ Programming Penn Wu, PhD 195

19 D. stockprice 6. Given the following code segment, which statement is correct? ref class Fruit... double size; private: int count; ; A. A derived class can inherit only the "size" variable. B. A derived class can inherit both "size" and "count" variables. C. A derived class can inherit only the "count" variable. D. A derived class cannot inherit "size" and "count" variables. 7. Which function will be execution if you issue a area("3.5") statement? A. int area(int x) // B. double area(double x) // C. String^ area(string^ x) // D. void area() // 8. Given the following code segment, which statement is correct? void print(int i) MessageBox::Show(i); void print(double f) MessageBox::Show(f); A. There are two functions, both are named "print", and they do not overload each other. B. There are two functions called "print", and they can only accept a double data because the one with int is overloaded to accept a double data. C. There is a function called "print", it accepts an int type. There is another function, also called "print", that is meant to overload the previous one to accept a double type of data as input. D. They are two functions with the same name, the overloading keeps the "print" function from accepting either int or double type data as input. 9. Given the following code, which statements in the main() method can yield a message "The sky is blue."? ref class base void func() MessageBox::Show("The sky was blue."); ; ref class child1 : public base void func() MessageBox::Show("The sky is not blue."); ; ref class child2 : public base void func() MessageBox::Show("The sky is blue."); ; A. base^ obj; obj->func(); B. child1^ obj; obj->func(); C. child2^ obj; obj->func(); D. child^ obj; obj->func(); Visual C++ Programming Penn Wu, PhD 196

20 10. Given the following code, which statements in the main() method can yield a message "A Child object!"? class Parent void display() MessageBox::Show("A Parent object!"); ; class Child : public Parent void display() MessageBox::Show("A Child object!"); ; A. Child^ c1; c1->display(); B. Parent^ C1; C1->display(); C. Child : Parent^ c1; c1->display(); D. Parent::Child^ C2; C1->display(); Visual C++ Programming Penn Wu, PhD 197

21 Lab #7 Inheritance and Polymorphism Learning Activity #1: Inheritance 1. Launch the Developer Command Prompt (not the regular Command Prompt) and change to the C:\cis223 directory. 2. Under the C:\cis223 directory, use Notepad to create a new file named lab7_1.cpp with the following contents: #include "InputBox.cpp" ref class GetFoot // base class protected: int feet; GetFoot() // defaut constructor feet = Convert::ToInt32(InputBox::Show("Enter the feet:")); ; ref class GetInch : GetFoot // derived class protected: int inch; int height; // member of GetInch GetInch() // default constructor inch = Convert::ToInt32(InputBox::Show("Enter the inch:")); height = feet * 12 + inch; // inherit feet from GetFoot ; String^ str = ""; GetInch^ g1 = gcnew GetInch; MessageBox::Show("You are " + g1->height + " inches tall."); return 0; 3. Open the Visual Studio (2010) Command Prompt, type cl /clr lab6_1.cpp /link /subsystem:windows /ENTRY:main and press [Enter] to compile. C:\cis223>cl /clr lab6_1.cpp /link /subsystem:windows /ENTRY:main 4. Test the program, the output looks: Visual C++ Programming Penn Wu, PhD 198

22 and and 5. Download the assignment template, and rename it to lab7.doc if necessary. Capture a screen shot similar to the above figure and paste it to the Word document named lab7.doc (or.docx). Learning Activity #2: Inheritance 1. Launch the Developer Command Prompt (not the regular Command Prompt) and change to the C:\cis223 directory. 2. Use Notepad to create a new file named lab7_2.cpp with the following contents: ref class Car // base class // open to the entire program int mpg; int tanksize; protected: int mileage() return mpg * tanksize; private: // not open to child class int securitycode; ; ref class Sedan : public Car // declare Sedan a child of Car int tirenumber; int ml; Sedan() tirenumber = 4; mpg = 34; tanksize = 16; ml = mileage(); void TurboIt() mpg = mpg * 1.5; ; String^ str = "Car\tMPG\tTank Size\tTires\tMileage\n"; Visual C++ Programming Penn Wu, PhD 199

23 Sedan^ s1 = gcnew Sedan; // instance of Sedan s1->turboit(); // member of Sedan only str += "s1\t" + s1->mpg + "\t" + s1->tanksize + "\t"; str += s1->tirenumber + "\t" + s1->ml + "\n"; Car^ s2 = gcnew Car; str += "s2\t" + s2->mpg + "\t" + s2->tanksize + "\n"; Car^ s3 = gcnew Sedan; str += "s3\t" + s3->mpg + "\t" + s3->tanksize + "\t"; //str += s3->tirenumber + "\t" + s3->ml + "\n"; MessageBox::Show(str); 3. Compile and test the program. 4. Capture a screen shot similar to the above figure and paste it to the Word document named lab7.doc (or.docx). Learning Activity #3: Multiple layer inheritance 1. Use Notepad to create a new file named lab7_3.cpp with the following contents: #include "InputBox.cpp" ref class TicketPrice // parent double unitprice; double saleprice; TicketPrice() // default constructor unitprice = Convert::ToDouble(InputBox::Show("Unit price: ")); ; ref class DiscountPrice : TicketPrice // child double discountrate; DiscountPrice() // default constructor discountrate = Convert::ToDouble(InputBox::Show("Discount rate (%): ")) * 0.01; saleprice = unitprice * (1- discountrate); Visual C++ Programming Penn Wu, PhD 200

24 ; ref class SalePrice : DiscountPrice // grandchild private: double roundit(double n) return Math::Round(n, 2); protected: double taxrate; double finalprice; double showtaxrate() return taxrate; SalePrice() // default constructor taxrate = Convert::ToDouble(InputBox::Show("Tax rate (%): ")) * 0.01; finalprice = saleprice * (1 + taxrate); finalprice = roundit(finalprice); ; String^ str = "Unit Price\tDiscount\tTax\tSale Price\n"; SalePrice^ s1 = gcnew SalePrice(); str += "$" + s1->unitprice + "\t$"; str += s1->discountrate + "\t" + s1->showtaxrate() + "\t$" + s1->finalprice; MessageBox::Show(str); return 0; 2. Compile and test the program. and and and 3. Capture a screen shot similar to the above figure and paste it to the Word document named lab7.doc (or.docx). Learning Activity #4: Subclass Polymorphism 1. Use Notepad to create a new file named lab7_4.cpp with the following contents: Visual C++ Programming Penn Wu, PhD 201

25 ref class Socal // base class protected: int staff, faculty; void setvalues(int x, int y) staff=x; faculty=y; int total() // form 1 return (staff + faculty); String^ getcount() return staff + "\t" + faculty + "\t" + total() + "\n"; ; ref class ShermanOaks : public Socal ; // an empty class ref class Pomona: public Socal // derived class int total() // form 2 return (staff * faculty * 0.6); ; ref class LongBeach: public Socal // derived class int total() // form 3 return (staff + faculty / 2); ; Pomona^ s1 = gcnew Pomona(); s1->setvalues(15, 7); LongBeach^ s2 = gcnew LongBeach(); s2->setvalues(12, 6); ShermanOaks^ s3 = gcnew ShermanOaks(); s3->setvalues(10, 4); String^ str = " Employees Count \n"; str += "Staff\tFaculty\tTotal\n"; str += s1->getcount(); str += s2->getcount(); str += s3->getcount(); MessageBox::Show(str); Visual C++ Programming Penn Wu, PhD 202

26 return 0; 2. Compile and test the program. 3. Capture a screen shot similar to the above figure and paste it to the Word document named lab7.doc (or.docx). Learning Activity #5: 1. Use Notepad to create a new file named lab7_5.cpp with the following contents: #include "InputBox.cpp" ref class Sum String^ result; Sum(int n) int sum = 0; for (int i=1; i<=n; i++) sum = sum + i; result = sum + "\n"; ; ref class Factorial String^ result; Factorial(int n) int factorial = 1; for (int i=1; i<=n; i++) factorial = factorial * i; result = factorial + "\n"; ; Visual C++ Programming Penn Wu, PhD 203

27 ref class Average String^ result; Average(int n) double avg; for (int i=1; i<=n; i++) avg = avg + i; result = (avg / n) + "\n"; ; ref class Mymath String^ str; Mymath() String^ option = InputBox::Show("1 - Average, 2 - Factorial, 3 - Sum. [1/2/3]:"); int n = Convert::ToInt32(InputBox::Show("Enter an integer:")); if (option == "1") Average^ a1 = gcnew Average(n); str = a1->result; if (option == "2") Factorial^ f1 = gcnew Factorial(n); str = f1->result; if (option == "3") Sum^ s1 = gcnew Sum(n); str = s1->result; ; Mymath^ m1 = gcnew Mymath(); MessageBox::Show(m1->str); 2. Compile and test the program. and and Visual C++ Programming Penn Wu, PhD 204

28 3. Capture a screen shot similar to the above figure and paste it to the Word document named lab7.doc (or.docx). Submittal 1. Complete all the 5 learning activities and the programming exercise in this lab. 2. Create a.zip file named lab7.zip containing ONLY the following self-executable files. Upload the.zip file to Dropbox. lab7_1.exe lab7_2.exe lab7_3.exe lab7_4.exe lab7_5.exe lab7.doc (or lab7.docx or.pdf) [You may be given zero point if this Word document is missing] 3. Upload the zipped file to Question 11 of Assignment 07 as response. 4. Upload ex07.zip file to Question 12 as response. Note: You will not receive any credit if you submit file(s) to the wrong question. Programming Exercise 07: 1. Launch the Developer Command Prompt. 2. Use Notepad to create a new text file named ex07.cpp. 3. Add the following heading lines (Be sure to use replace [YourFullNameHere] with the correct one). //File Name: ex07.cpp //Programmer: [YourFullNameHere] 4. Given the following class mypoly with a function func() which is the first form (form 1), write codes to create three other forms of the func() function. Particularly, one integer form, one double form, one that takes two string parameters. class mypoly String^ func(string^ v1) //form1 return "I took " + v1 + "."; //YourCodeHere ; Form Function Value of n, v1, v2 1 Return a text I took v1. v1: CIS223 where v1 is a value given by the main() method. 2 Return a text I am an 15 integer n. where n is a value given by the main() method. 3 Return a text I am a double value n. where n is a value given by the main() method. 4 Return a text I am a v1 and a v2. where v1 and v2 are string values given by the main() method. v1: student v2: good citizen 5. In the main() method, create a mypoly object named obj. Use this obj object as reference to call each of the four forms of func() function with the value(s) specified in the above table. You must clearly apply polymorphism to the codes to earn the credit, as do the examples provided in the lecture note. [Hint: you may have to use \n to create new lines] 6. The output should looks: Visual C++ Programming Penn Wu, PhD 205

29 7. Compile the source code to produce executable code. 8. Download the programming exercise template, and rename it to ex07.doc if necessary. Capture Capture a screen similar to the above one and paste it to the Word document named ex07.doc (or.docx). 9. Compress the source file (ex07.cpp), executable code (ex07.exe), and Word document (ex07.doc) to a.zip file named ex07.zip. Grading criteria: You will earn credit only when the following requirements are fulfilled. No partial credit is given. You successfully submit both source file and executable file. Your source code must be fully functional and may not contain syntax errors in order to earn credit. Your executable file (program) must be executable to earn credit. You will receive 0 credit if you simply display the messages without applying polymorphism in your code. Threaded Discussion Note: Students are required to participate in the thread discussion on a weekly basis. Student must post at least two messages as responses to the question every week. Each message must be posted on a different date. Grading is based on quality of the message. Question: Class, if you have write a Visual C++ application for three different types of platform, a Windowsbased desktop, a Windows-based tablet, and a Windows-based smartphone, how would you apply the concept of inheritance and polymorphism to the coding design of your application? [There is never a right-or-wrong answer for this question. Please free feel to express your opinion.] Be sure to use proper college level of writing. Do not use texting language. Visual C++ Programming Penn Wu, PhD 206