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.NET Framework Built-In Classes
 

Namespaces
 

Introduction

A namespace is a section of code that is recognized with a name. A namespace allows a programmer or a group of programmers who work with others to create code with names that don't conflict with code of the other programmers or other groups.

As mentioned already, a namespace is a section of code. Therefore, it must be created in a file before being used.

Creating a Namespace

The formula to create a namespace is:

Namespace name
    
End Namespace

As you can see, the creation of a namespace starts with the Namespace keyword and ends with the End Namespace expression. On the right side of the starting Namespace keyword, enter a name. The name follows the rules we have used so far for names in the Visual Basic language. Here is an example:

Namespace Census

End Namespace

The section between the starting Namespace line and End Namespace is the body of the namespace. In this body, you can write code as you want. For example, you can create a class in it. Here is an example:

Namespace Geometry
    Public Class Rectangle

    End Class
End Namespace

Of course, in the body of the class, you can write the necessary code. Here is an example:

Namespace Geometry
    Public Class Rectangle
        Public Width As Double
        Public Height As Double

        Public Function Perimeter() As Double
            Return (Width + Height) * 2
        End Function

        Public Function Area() As Double
            Return Width * Height
        End Function
    End Class
End Namespace

Accessing Members of a Namespace

The variables, procedures, and classes created inside a namespace can be referred to as its members.

To access a member of a namespace, you can use the period operator. To do this, where you want to access the member, type the name of the namespace, followed by a period, followed by the desired member of the namespace. Here is an example:

Namespace Geometry
    Public Class Rectangle
        
    End Class
End Namespace

Module Exercise

    Public Function Main() As Integer
        Geometry.Rectangle

        Return 0
    End Function

End Module

In the same way, wherever you want to access a member of a namespace, you can simply qualify it. Once the member has been qualified, you can use it as we saw in previous lessons. Here are examples:

Namespace Geometry
    Public Class Rectangle
        Public Width As Double
        Public Height As Double

        Public Function Perimeter() As Double
            Return (Width + Height) * 2
        End Function

        Public Function Area() As Double
            Return Width * Height
        End Function
    End Class
End Namespace

Module Exercise

    Public Function Main() As Integer
        Dim Rect As Geometry.Rectangle
        Rect = New Geometry.Rectangle

        Rect.Width = 40.18
        Rect.Height = 28.46


        MsgBox("Rectangle Characteristics" & vbCrLf & _
               "Width:" & vbTab & vbTab & FormatNumber(Rect.Width) & vbCrLf & _
               "Height:" & vbTab & vbTab & FormatNumber(Rect.Height) & vbCrLf & _
               "Perimeter:" & vbTab & FormatNumber(Rect.Perimeter()) & vbCrLf & _
               "Area:" & vbTab & vbTab & FormatNumber(Rect.Area()))
        Return 0
    End Function

End Module

In the same way, you can create as many members as you want in the body of a namespace.

In the above code, we create our namespace in the same file that contains the Main() function. To better manage your code, you can create your namespaces in different files. Here is an example:

Namespace Geometry
    Public Class Rectangle
        Public Width As Double
        Public Height As Double

        Public Function Perimeter() As Double
            Return (Width + Height) * 2
        End Function

        Public Function Area() As Double
            Return Width * Height
        End Function
    End Class

    Public Class Triangle
        Public Base As Double
        Public Height As Double

        Public Function Area() As Double
            Return Base * Height / 2
        End Function
    End Class
End Namespace

In the same way, you can create as many namespaces in as many files as you want. A namespace can be created in more than one file.

Importing a Namespace

When accessing each member of a namespace, you can qualify its name wherever you want to use it. Here are examples that use the above namespace that was created in a separate file:

Module Exercise

    Public Function Main() As Integer
        Dim Rect As Geometry.Rectangle = New Geometry.Rectangle

        Rect.Width = 40.18
        Rect.Height = 28.46

        MsgBox("Rectangle Characteristics" & vbCrLf & _
               "Width:" & vbTab & vbTab & FormatNumber(Rect.Width) & vbCrLf & _
               "Height:" & vbTab & vbTab & FormatNumber(Rect.Height) & vbCrLf & _
               "Perimeter:" & vbTab & FormatNumber(Rect.Perimeter()) & vbCrLf & _
               "Area:" & vbTab & vbTab & FormatNumber(Rect.Area()))

        Dim Tri As Geometry.Triangle = New Geometry.Triangle

        Tri.Base = 36.09
        Tri.Height = 28.46

        MsgBox("Triangle Characteristics" & vbCrLf & _
               "Base:" & vbTab & vbTab & FormatNumber(Tri.Base) & vbCrLf & _
               "Height:" & vbTab & vbTab & FormatNumber(Tri.Height) & vbCrLf & _
               "Area:" & vbTab & vbTab & FormatNumber(Tri.Area()))
        Return 0
    End Function

End Module

Instead of qualifying each member, you can import the namespace in the file where you want to use it. To do this, in the top section of the file, type Imports followed by the name of the namespace.

Nesting a Namespace

You can create one namespace inside of another namespace. This is referred to as nesting the namespace. To nest a namespace, create its body in the body of an existing namespace. Here is an example:

Namespace Geometry    

    Namespace Quadrilateral
        
    End Namespace

End Namespace

Inside the new namespace, you can implement the behavior you want. For example, you can create a class. The parent namespace is still its own namespace and can contain any necessary thing. Here is an example:

Namespace Geometry
    Friend Class Triangle
        Public Base As Double
        Public Height As Double

        Public Function Area() As Double
            Return Base * Height / 2
        End Function
    End Class

    Namespace Quadrilateral
        Public Class Rectangle
            Public Width As Double
            Public Height As Double

            Public Function Perimeter() As Double
                Return (Width + Height) * 2
            End Function

            Public Function Area() As Double
                Return Width * Height
            End Function
        End Class
    End Namespace

End Namespace

To access a member of the parent namespace, you can qualify it as we saw previously. To access a member of the nested namespace outside the parent, type the name of the nesting namespace, followed by a period, followed by the name of the nested namespace, followed by a period, and followed by the member you want to access. Here are examples:

Namespace Geometry
    Friend Class Triangle
        Public Base As Double
        Public Height As Double

        Public Function Area() As Double
            Return Base * Height / 2
        End Function
    End Class

    Namespace Quadrilateral
        Public Class Rectangle
            Public Width As Double
            Public Height As Double

            Public Function Perimeter() As Double
                Return (Width + Height) * 2
            End Function

            Public Function Area() As Double
                Return Width * Height
            End Function
        End Class
    End Namespace

End Namespace

Module Exercise

    Public Function Main() As Integer
        Dim Tri As Geometry.Triangle = New Geometry.Triangle

        Tri.Base = 36.09
        Tri.Height = 28.46

        MsgBox("Triangle Characteristics" & vbCrLf & _
               "Base:" & vbTab & vbTab & FormatNumber(Tri.Base) & vbCrLf & _
               "Height:" & vbTab & vbTab & FormatNumber(Tri.Height) & vbCrLf & _
               "Area:" & vbTab & vbTab & FormatNumber(Tri.Area()))

        Dim Rect As Geometry.Quadrilateral.Rectangle

        Rect = New Geometry.Quadrilateral.Rectangle
        Rect.Width = 40.18
        Rect.Height = 28.46

        MsgBox("Rectangle Characteristics" & vbCrLf & _
               "Width:" & vbTab & vbTab & FormatNumber(Rect.Width) & vbCrLf & _
               "Height:" & vbTab & vbTab & FormatNumber(Rect.Height) & vbCrLf & _
               "Perimeter:" & vbTab & FormatNumber(Rect.Perimeter()) & vbCrLf & _
               "Area:" & vbTab & vbTab & FormatNumber(Rect.Area()))

        Return 0
    End Function

End Module

In the same way:

  • You can create as many namespaces as you want inside of a nesting namespace
  • You can nest as many namespaces in as many nesting namespaces

Remember how to backwardly qualify the name of a member of a nested namespace. If the namespace exists in a separate file and you want to import it, type the Imports keyword, followed by the name of the parent namespace, followed by a period, and followed by the nested namespace. In the same way, you can import any nested namespace, as long as you appropriately qualify its name.

The System Namespace

To make programming in Visual Basic easier, many classes were created and stored in various namespaces. Each namespace is used to provide specific instructions.

One of the most regularly used namespaces in the Visual Basic language is called System. Inside of the System namespace is a class called Console. The Console class is used to display things on the console screen also called the DOS window.

The Console class contains procedures to display information on the screen or to retrieve information from the user who types it in the DOS window. The procedure that is used to display text on the screen is called Write. To use Write(), inside of the parentheses, type the sentence between double-quotes. Here is an example:

Module Exercise

    Public Function Main() As Integer

        System.Console.Write("Welcome")

        Return 0
    End Function

End Module

Besides Write(), the Console class also provides a procedure called WriteLine(). Here is an example:

Module Exercise

    Public Function Main() As Integer

        System.Console.WriteLine()

        Return 0
    End Function

End Module

The difference is that, after displaying something on the screen, the Write() method keeps the caret on the same line but WriteLine() transfers the caret to the next line.

We mentioned that, to access a member of a namespace, you could type the name of the namespace, followed by a period, and followed by the name of the member. This technique is referred to as qualifying a member of a namespace. This can be long ins some cases. Instead of qualifying a member of a namespace every time you want to use it, you can import the namespace into the file where you want to access its member(s). Here is an example:

Imports System

Module Exercise

    Public Function Main() As Integer

        Console.WriteLine()

        Return 0
    End Function

End Module

Built-In Classes: The Object Class
 

Introduction

The .NET Framework is a huge library made of various classes and constants you can directly use in your application without necessarily explicitly loading an external library. To start, this main library provides a class called Object.

When you create a class, it automatically inherits its primary characteristics from the parent of all classes: Object.

Equality of Two Class Variables

When you declare and initialize two variables, one of the operations you may want to subsequently perform is to compare their value. To support this operation, the Object class provides its children with a method called Equals. The Equals() method comes in two versions. The first has the following syntax: 

Public Overridable Function Equals(obj As Object) As Boolean

This version allows you to call the Equals() method on a declared variable and pass the other variable as argument. Here is an example: 

Imports System

Module Exercise

    Public Function Main() As Integer
        ' First book
        Dim NumberOfPages1 As Integer = 422
        ' Second book
        Dim NumberOfPages2 As Integer = 858
        ' Third book
        Dim NumberOfPages3 As Integer = 422

        If NumberOfPages1.Equals(NumberOfPages2) = True Then
            Console.WriteLine("The first and the second books " & _
                              "have the same number of pages")
        Else
            Console.WriteLine("The first and the second books " & _
                              "have different number of pages")
        End If

        If NumberOfPages1.Equals(NumberOfPages3) = True Then
            Console.WriteLine("The first and the third books " & _
                              "have the same number of pages")
        Else
            Console.WriteLine("The first and the third books " & _
                              "have different number of pages")
        End If

        Return 0
    End Function

End Module

This would produce:

The first and the second books have different number of pages
The first and the third books have the same number of pages

The first version of the Object.Equals method is declared as Overridable, which means you can override it if you create your own class. The second version of the Object.Equals() method is:

Public Shared Function Equals(objA As Object, objB As Object) As Boolean

As a Shared method, to use it, you can pass the variables of the two classes whose values you want to compare.

In both cases, if the values of the variables are similar, the Equals() method returns true. If they are different, the method returns false. If you are using the Equals() method to compare the variables of two primitive types, the comparison should be straight forward. If you want to use this methods on variables declared from your own class, you should provide your own implementation of this method.

Stringing a Class

In previous lessons, we learned that, to convert the value of a variable declared from a primitive type to a string, you could call the ToString() function. Here is an example:

Imports System

Module Exercise

    Public Function Main() As Integer
        Dim NumberOfPages As Integer = 422

        Console.Write("Number of Pages: ")
        Console.WriteLine(NumberOfPages.ToString())
        Return 0
    End Function

End Module

In many programming languages, programmers usually have to overload an (extractor) operator to display the value(s) of class' variable to the screen. The Object class provides an alternative to this somewhat complicated solution, through the ToString() method. It syntax is:

Public Overridable Function ToString As String

Although the Object class provides this method as non abstract, its implemented version is more useful if you use a primitive type such as Integer, Double and their variances or a string variable. The best way to rely on it consists of overriding it in your own class if you desire to use its role.

Boxing and Un-Boxing

When we study inheritance, we will learn that all data types used in a C# program are "based on" an object called object. As introduced earlier, you can use this data type to declare a variable that would hold any type of value. Because this is some type of a "universal" data type, it can also be initialized with any value. Here are examples:

Imports System

Module Exercise

    Public Function Main() As Integer
        Dim Number As Object
        Dim Thing As Object

        Number = 244
        Thing = "Professor Kabba"

        Console.WriteLine(Number)
        Console.WriteLine(Thing)
        Return 0
    End Function

End Module

This would produce:

244
Professor Kabba

As you can see, when an object variable is initialized, the compiler finds out the type of value that was assigned to it. This is referred to as boxing. This mechanism is transparently done in Visual Basic.

If you declare a variable using a primitive data type (Integer, Single, Double, etc), at one time, you may be interested in converting the value of that variable into an Object. Here is an example:

Imports System

Module Exercise

    Public Function Main() As Integer
        Dim Number As Integer = 244
        Dim Thing As Object = Number

        Number = 244
        Thing = Number

        Console.WriteLine(Number)
        Console.WriteLine(Thing)
        Return 0
    End Function

End Module

This would produce:

244
244

This operation is referred to as unboxing. As you can see, this operation is performed transparently.

Finalizing a Variable

While a constructor, created for each class, is used to instantiate a class. The Object class provides the Finalize() method as a type of destructor.

Built-In Classes: The Random Class
 

Introduction

Imagine you have a series of numbers, such these: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. Imagine you want to select one of these numbers, any of them. A number is referred to as random if it has been selected from a pool without a specific pattern to follow. For example, if you decide to select the value 17 from this list, if there was an exact reason that number was selected, then it is not considered random. In reality, it is difficult for a number to qualify as random. For this reason, most random numbers are referred to as pseudo-random.

Getting a Random Number

To support the ability to create or choose a random number, the .NET Framework provides the Random class. To start, you can declare a variable of this class, using one of its two constructors. Here is an example that uses the default constructor:

Module Exercise

    Public Function Main() As Integer
        Dim rndNumbers As Random = New Random

        Return 0
    End Function

End Module

After declaring the variable, you can start getting numbers from it. To do this, you call the Next() method, which is overloaded in three versions. One of the versions of this method takes no argument and its syntax is:

Public Overridable Function Next As Integer

This method generates a randomly selected integer between 0 and the MinValue value of the Integer data type. Here is an example:

REM Imports System

Module Exercise

    Public Function Main() As Integer
        Dim rndNumbers As Random = New Random
        Dim rndNumber As Integer = rndNumbers.Next()

        Console.Write("Number: ")
        Console.WriteLine(rndNumber.ToString())

        Return 0
    End Function

End Module

Here is an example of running the program:

Number: 1369872590
Press any key to continue . . .

In the same way, you can call this version of the Next() method repeatedly to get random. Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim nbr As Integer
        Dim rndNumber As Integer = 0
        Dim rndNumbers As Random = New Random

        For nbr = 1 To 9
            rndNumber = rndNumbers.Next()
            Console.Write("Number: ")
            Console.WriteLine(rndNumber.ToString())
        Next

        Return 0
    End Function

End Module

Here is an example of running the program:

Number: 1924504148
Number: 1257846191
Number: 424740120
Number: 1009211682
Number: 544356245
Number: 708951978
Number: 759684741
Number: 1325535324
Press any key to continue . . .

The Seed of a Random Number

Consider the following program:

Module Exercise

    Public Function Main() As Integer
        Dim rndNumbers As Random = New Random
        Dim rndNumber As Integer = rndNumbers.Next()

        Console.Write("Number: ")
        Console.WriteLine(rndNumber.ToString())

        Return 0
    End Function

End Module

Here is an example of running the program:

Number: 573991745
Press any key to continue . . .

Here is another example of running the same program:

Number: 334223329
Press any key to continue . . .

Notice that the numbers generated are different. When creating a program that repeatedly gets a series of random numbers, you may (or may not) want the Random class to generate the same number over and over again. A seed is a constant value that controls whether a random generation would produce the same result every time it occurs. For example, using a seed, you can impose it upon the Random class to generate the same number every time the Next() method is called. To support the ability to use a seed, the Random class is equipped with a second constructor whose syntax is:

Public Sub New(Seed As Integer)

Based on this, to specify a seed, when declaring a Random variable, pass a constant integer to the constructor. Here is an example:

Module Exercise

    Public Function Main() As Integer
        Dim rndNumbers As Random = New Random(20)
        Dim rndNumber As Integer = rndNumbers.Next()

        Console.WriteLine("Number: {0}", rndNumber)

        Return 0
    End Function

End Module

Here is one example of running the program:

Number: 375271809
Press any key to continue . . .

Here is another example of running the same program:

Number: 375271809
Press any key to continue . . .

Notice that the numbers are the same. Consider this program also:

REM Imports System

Module Exercise

    Public Function Main() As Integer
        Dim nbr As Integer
        Dim rndNumber As Integer = 0
        Dim rndNumbers As Random = New Random(20)

        For nbr = 1 To 5
            rndNumber = rndNumbers.Next()
            Console.Write("Number: ")
            Console.WriteLine(rndNumber.ToString())
        Next

        Return 0
    End Function

End Module

Here is one example of running the program:

Number: 375271809
Number: 1472524622
Number: 1605850688
Number: 1776011503
Press any key to continue . . .

Here is another example of running the same program:

Number: 375271809
Number: 1472524622
Number: 1605850688
Number: 1776011503
Press any key to continue . . .

Notice that the sequences are the same. In both cases, this indicates that, if you specify a seed, the Random class would generate the same number or the same sequence of numbers.

Generating Random Numbers in a Range of Numbers

So far, we have been using any number that would fit an integer. In some assignments, you may want to restrict the range of numbers that can be extracted. Fortunately, the Random class allows this. Using the Random class, you can generate random positive numbers up to a maximum of your choice. To support this, the Random class is equipped with another version of the Next() method whose syntax is:

Public Overridable Function Next(maxValue As Integer) As Integer

The argument to pass to the method determines the highest integer that can be generated by the Next() method. The method returns an integer. Here is an example that generates random numbers from 0 to 20:

REM Imports System

Module Exercise

    Public Function Main() As Integer
        Dim nbr As Integer
        Dim rndNumber As Integer = 0
        Dim rndNumbers As Random = New Random

        For nbr = 1 To 9
            rndNumber = rndNumbers.Next(20)
            Console.Write("Number: ")
            Console.WriteLine(rndNumber.ToString())
        Next

        Return 0
    End Function

End Module

Here is an example of running the program:

Number: 1
Number: 7
Number: 1
Number: 16
Number: 14
Number: 19
Number: 3
Number: 1
Press any key to continue . . .

The above version of the Next() method generates numbers starting at 0. If you want, you can specify the minimum and the maximum range of numbers that the Next() method must work with. To support this, the Random class is equipped with one more version of this method and that takes two arguments. Its syntax is:

Public Overridable Function Next(minValue As Integer, _
				 maxValue As Integer) As Integer

The first argument specifies the lowest value that can come from the range. The second argument holds the highest value that the Next() method can generate. Therefore, the method would operate between both values. Here is an example that generates random numbers from 6 to 18: 

Module Exercise

    Public Function Main() As Integer
        Dim nbr As Integer
        Dim rndNumber As Integer = 0
        Dim rndNumbers As Random = New Random

        For nbr = 1 To 9
            rndNumber = rndNumbers.Next(6, 18)
            Console.Write("Number: ")
            Console.WriteLine(rndNumber.ToString())
        Next

        Return 0
    End Function

End Module

Here is an example of running the program:

Number: 17
Number: 9
Number: 8
Number: 15
Number: 10
Number: 9
Number: 13
Number: 11
Press any key to continue . . .

Class Destruction
 

Garbage Collection

When you initialize a variable using the New operator, you are in fact asking the compiler to provide you some memory space in the heap memory. The compiler is said to "allocate" memory for your variable. When that variable is no longer needed, for example when your program closes, it (the variable) must be removed from memory and the space it was using can be made available to other variables or other programs. This is referred to as garbage collection.

The .NET Framework solves the problem of garbage collection by letting the compiler "clean" memory after you. This is done automatically when the compiler judges it necessary so that the programmer doesn't need to worry about this issue.

Class Finalization

When you declare a variable based on a class, the compiler allocates memory for it. This portion of memory would be available and used while the program is running and as long as the compiler judges this necessary. While the program is running, the instance of the class uses or consumes the computer's resources as necessary. When the object is not needed anymore, for example when the program terminates, the object must be destroyed, the memory it was using must be emptied to be made available to other programs on the computer, and the resources that the object was using should (must) be freed to be restored to the computer so they can be used by other programs. To make this possible, the Object class is equipped with a method called Finalize that is protected and therefore made available to all descendant classes of the .NET Framework.

The syntax of the Object.Finalize() method is:

Overrides Protected Sub Finalize()

The Finalize() method is automatically called when an instance of a class is not needed anymore. In all of the classes we have used so far, this method was transparently called when the compiler judged that the instance of the class was not used anymore. If you don't want this method to be called, call the  

Public Shared Sub SuppressFinalize(ByVal obj As Object)

In most cases, you can let the compiler call the Finalize() method when the time comes.
 
 
 

Custom Libraries
 

Introduction

If you cannot find a function you want, you can create one and be able to use it. If you plan to use such a function over and over again in different programs, you can create a library and store the function in it. You can even create one or a series of commercial functions and be able to distribute or sell it through a library.

A library is a program that contains procedures and/or other resources that other programs can use. Such a program is created with the same approach as the programs we have created so far. Because a library is not an executable, it does not need the Main() procedure. A library usually has the extension .dll.

Creating a Library

A library can be made of a single file or as many files as necessary. A file that is part of a library can contain one or more procedures (or classes). Each procedure (or class) should implement a behavior that can eventually be useful and accessible to other procedures (or classes). The contents of a library are created exactly like those we have used so far. Everything depends on how you compile it.

To create a library:

  • On the main menu of Microsoft Visual Studio, you can click File -> New -> Project
  • On the Start Page, on the right side of Create, you can click Project
  • On the Standard toolbar, you can click the New Project button or click the arrow of the New Project button and click New Project

In the Templates list of the New Project dialog box, click Class Library. Accept or specify the name and click OK. Once the starting project has been generated, write the necessary code. To compile it, on the main menu, click Build -> Build Solution. If you were working from the command prompt, you would execute the following command:

vbc /target:library NameOfFile.vb

After doing this, a library with the name of the file and the extension .dll would be created. If you use the above technique, the new library would be created using the name of the file. If you are working from the Command Prompt, to compile the project and create a custom name, use the following syntax: 

vbc /target:library /out:DesiredNameOfLibrary.dll NameOfFile.vb

Here is an example:

vbc /target:library /out:Arithmetic.dll exo.vb

Practical LearningPractical Learning: Creating a Library
  1. Start Microsoft Visual Studio
  2. To start a new project, on the main menu, click File -> New -> Project...
  3. In the Project Types list, make sure Visual Basic is selected.
    In the Templates List, click Class Library
  4. Change the Name to Arithmetic and click OK
  5. In the Solution Explorer, right-click Module.vb and click Rename
  6. Type Operations.vb and press Enter
  7. Change the file as follows:
      
    Public Class Arithmetic
    Function Add(ByVal x As Double, ByVal y As Double) As Double
        Return x + y
    End Function

    Function Subtract(ByVal x As Double, ByVal y As Double) As Double
        Return x - y
    End Function

    Function Multiply(ByVal x As Double, ByVal y As Double) As Double
        Return x * y
    End Function

    Function Divide(ByVal x As Double, ByVal y As Double) As Double
        If y = 0 Then Return 0
        Return x / y
    End Function
End Class
  8. To create the library, on the main menu, click Build -> Build Arithmetic
  9. To start another project, on the main menu, click File -> New -> Project...
  10. In the Templates List, click Console Application
  11. Change the Name to Algebra and click OK
  12. In Windows Explorer or My Documents, locate the Arithmetic folder that contains the library project. Access a sub-folder of the same name, followed by the bin sub-folder, and followed by the Debug sub-folder
  13. Right-click Arithmetic.dll and click Copy
  14. Still in Windows Explorer or My Documents, locate the Algebra folder that contains the current project. Right-click the sub-folder of the same name and click Paste
  15. In the Solution Explorer, right-click Algebra and click Add Reference...
  16. In the Add Reference dialog box, click the Browse tab
  17. Use the Look In combo box to locate and select a sub-folder named Algebra in the current project
  18. Click Arithmetic.dll and click OK
  19. In the Solution Explorer, right-click Module1.vb and click Rename
  20. Type Exercise.vb and press Enter. Accept to make all necessary changes
  21. Change the the file as follows:
      
    Imports Operations

Module Exercise

    Public Function Main() As Integer
        Dim Result As Double
        Dim Oper As Arithmetic
        Dim Number1 As Double, Number2 As Double

        Number1 = 244.58
        Number2 = 5082.88
        Oper = New Arithmetic
        Result = Oper.Add(Number1, Number2)

        MsgBox(Number1 & " + " & Number2 & " = " & Result)
        Return 0
    End Function

End Module
  22. To execute the project, on the main menu, click Debug -> Start Without Debugging
 
 
   
 
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