SD6502代做、代写C++语言编程

日期：2024-10-23 09:40

SD6502 Programming II 1

Lab Work

continued from last lab(week 5)

Task 1:Inheritance

1. Let’s add a few more classes to the PolytechLibrary which you created in last lab session.

(a) Add a class and name it Teacher.cs

(b) Add attributes(fields) such as FirstName, LastName, Email Address and Subject as properties.

(c) Add another class name it Student.cs

(d) Add some fields(properties), FirstName, LastName . . . .

Wait, didn’t you add same fields already for teacher class. Teacher and students have things in common

such as firstname, lastname, email address and so on. Unlike Teacher, students do not have

subject to teach. We can make use of a OO concept called inheritance here. What we can do is define

a class, say person, and put all the common fields (attributes) there. Then make Student and Teacher

classes inherit all the common attribute from Person class. Of course, we will add the unique fields of

their own in their class definition.

2. Add a class person

3. Add common attributes to Person class and remove those from Teacher and student class

public class Person {

public string FirstName { get; set; }

public string LastName { get; set; }

public string Email { get; set; }

}

Also,

Teacher and Student should now look like this,

public class Teacher : Person {

public string Subject { get; set; }

}

public class Student : Person {

}

Note: The class names Teacher and Student is followed by a colon and then Person. The Person

class is called base or parent class. Similarly Teacher and student classes are called derived or child

or subclass. Also, if you are working with VS 2022 replace internal keyword public. VS2022/.Net

framework 6 automatically adds internal keyword when you add a new class file.

.SD6502 Programming II 2

One other thing, if you don’t want others who are using the PolytechLibrary to be able to use the

Person class directly(by directly I mean creating an object and using it from their code) you can make

person class abstract. In this way you are making others to use Teacher and Student class directly

from their code.

4. Add a keyword abstract before the class keyword in the definition of person class

public abstract class Person {

public string FirstName { get; set; }

public string LastName { get; set; }

public string Email { get; set; }

}

Let’s add some attributes(feilds) to the empty Student class. A attribute called GradLevel to show

what level they are studying in. What type of data a GradLevel would hold ? In our polytech we

have level 5, level 7 and level 8 graduates. How would you model this fixed but discrete set of

data ? Enumeration datatype are perfectly suited in this situation. So let’s define a enum and call it

Gradlevels. Also, add a property to get and set Gradlevels field.

public class Student: Person {

public enum GradLevels {Level_5, Level_7, Level_8, Level_9 }

public GradeLevels GradLevel {get; set; }

}

Task 2: Working with derived class objects

Let’s go back to our PolytechFormApp. Double click the button to get the source code.

Try making it a new Person, i.e. create an object of Person class. Did you get any error why?

Create Teacher and Student objects and try and access all the fields.

Task 3:Abstract methods

Abstract classes are classes that are designed such that you can’t instantiate them or use them directly. The

same is true for abstract methods. An abstract method is a method with no code in it. Let’s say, for example,

we want to implement a method that will allow us to get a grade point average, but it’s going to be a different

computation depending on whether you’re talking about the teacher or the student. The student is going to

have the average of all the grades for the semester or the period or whatever time period we’re talking about

and the teacher’s grade point average is going to be the average grade point average for all of the students

in this class. So it makes sense to have two different, completely different implementations of a function by

the same name. So create the abstract method and then override it in each of the subclasses with specific

implementations for those classes.

.SD6502 Programming II 3

public abstract float ComputeGradeAverage ( ) ;

In Student class

public override float ComputeGradeAverage ( ) {

return 4.0f;

}

In Teacher class

public override float ComputeGradeAverage ( ) {

//TODO: fix the implementation later

return 0.0f;

}

Note: If a method(s) is declared abstract in base class all derived classes must have its definition (implementation).

In this case method ComputeGradeAverage must be implemented by Student and Teacher

classes. Otherwise, the code won’t compile. Also, note that you can also declare any method abstract in

non-abstract class.

Task 4: Testing the abstract method

Now that you have an abstract method and an overridden version of it in our two subclasses, why don’t we

take a look at what it looks like in our test program ?

Add two buttons and write code to test the overridden version of ComputeGradeAverage from both

classes.

Task 5:

Do all the examples exercise from Lecture slides. Codes are given here in the folder, try to understand:

1. How base and derived classes work in C#

2. How polymorphism is achieved in C#

3. What does extension methods do in C# and why it is useful?

Task 5:

Start working on your assignment.

Submission

NO submission needed. You will continue this work in the next lab. Show to your lab instructor when you

complete week 7 lab.

Credits: C# essentials, Bruce Van Horn.

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