Counting and Looping

1. Start Notepad and type the following in the empty file
    

   Imports System Module Module1 Enum TypeOfApplication NewDriversLicense = 1 UpgradeFromIDCard TransferFromAnotherState end enum Sub Main() Dim LastName As String, FirstName As String Dim OrganDonorAnswer As String, Gender As String Dim Sex As Char, DLClass As Char Dim iType As Integer Console.WriteLine(" -=- Motor Vehicle Administration -=-") Console.WriteLine(" --- Driver's License Application ---") Console.WriteLine(" - Select the type of application -") Console.WriteLine("1 - Applying for a brand new Driver's License") Console.WriteLine("2 - Applicant already had an ID Card and is applying for a Driver's License") Console.WriteLine("3 - Applicant is transferring his/her Driver's License from another state") Console.Write("Your Choice: ") iType = CInt(Console.ReadLine()) Console.Write("First Name: ") FirstName = Console.ReadLine() Console.Write("Last Name: ") LastName = Console.ReadLine() Console.Write("Sex(F=Female/M=Male): ") Sex = CChar(Console.ReadLine()) Console.WriteLine(" - Driver's License Class -") Console.WriteLine("A - All Non-commercial vehicles except motorcycles") Console.WriteLine("B - Non-commercial vehicles up to and including 26,001/more lbs.") Console.WriteLine("C - Cars, pick-up trucks, non-commercial vehicles 26,000 lbs.") Console.WriteLine("K - Mopeds") Console.WriteLine("M - Motorcycles") Console.Write("Your Choice: ") DLClass = CChar(Console.ReadLine()) Console.Write("Are you willing to be an Organ Donor(1=Yes/0=No)? ") OrganDonorAnswer = Console.ReadLine() If Sex = "f" Then Gender = "Female" ElseIf Sex = "F" Then Gender = "Female" ElseIf Sex = "m" Then Gender = "Male" ElseIf Sex = "M" Then Gender = "Male" Else Gender = "Unknown" End If Console.WriteLine("\n -=- Motor Vehicle Administration -=-") Console.WriteLine(" --- Driver's License Information ---") Console.Write("Type of Application: ") Select Case iType Case TypeOfApplication.NewDriversLicense Console.WriteLine("New Driver's License") Case TypeOfApplication.UpgradeFromIDCard Console.WriteLine("Upgrade From Identity Card") Case TypeOfApplication.TransferFromAnotherState Console.WriteLine("Transfer From Another State") Case Else Console.WriteLine("Not Specified") End Select Console.WriteLine("Full Name: {0} {1}", FirstName, LastName) Console.WriteLine("Sex: {0}", Gender) Select Case DLClass Case "a", "A" Console.WriteLine("Class: A") Case "b", "B" Console.WriteLine("Class: B") Case "c", "C" Console.WriteLine("Class: C") Case "k", "K" Console.WriteLine("Class: K") Case "m", "M" Console.WriteLine("Class: M") Case Else Console.WriteLine("Class: Unknown") End Select Console.Write("Organ Donor? ") If OrganDonorAnswer = "1" Then Console.WriteLine("Yes") ElseIf OrganDonorAnswer = "0" Then Console.WriteLine("No") Else Console.WriteLine("Invalid Answer") End If End Sub End Module

2. To save the file, on the main menu, click File -> Save
3. Locate and select your VBasic folder. Display it in the Save In combo box
4. Click the Create New Folder button
5. Create a folder named MVA2 and display it in the Save In combo box
6. Save the file as Exercise.vb
7. Open the Command Prompt and switch to the folder that contains the above Exercise.vb file
8. To compile the exercise, type vbc Exercise.vb and press Enter
9. To execute the exercise, type Exercise. Here is an example:
    

   C:\VBasic\MVA2>vbc Exercise.vb Microsoft (R) Visual Basic .NET Compiler version 7.10.3052.4 for Microsoft (R) .NET Framework version 1.1.4322.573 Copyright (C) Microsoft Corporation 1987-2002. All rights reserved. C:\VBasic\MVA2>Exercise -=- Motor Vehicle Administration -=- --- Driver's License Application --- - Select the type of application - 1 - Applying for a brand new Driver's License 2 - Applicant already had an ID Card and is applying for a Driver's License 3 - Applicant is transferring his/her Driver's License from another state Your Choice: 1 First Name: Leon Last Name: Schless Sex(F=Female/M=Male): m - Driver's License Class - A - All Non-commercial vehicles except motorcycles B - Non-commercial vehicles up to and including 26,001/more lbs. C - Cars, pick-up trucks, non-commercial vehicles 26,000 lbs. K - Mopeds M - Motorcycles Your Choice: k Are you willing to be an Organ Donor(1=Yes/0=No)? 1 -=- Motor Vehicle Administration -=- --- Driver's License Information --- Type of Application: New Driver's License Full Name: Leon Schless Sex: Male Class: K Organ Donor? Yes C:\VBasic\MVA2>

10. After using it, return to Notepad

The formula of the Do... Loop While loop is: Do     Statement(s) Loop While Condition This compiler first executes the Statement or Statements. After executing the Statement(s) section, the compiler checks the Condition. If the Condition is true, then the compiler returns to the Statement(s) and execute(s) it(them). The compiler keeps doing this check-execution gymnastic. AS LONG AS the Condition is true, the Statement(s) section will be executed and the Condition will be tested again. If the Condition is false or once the condition becomes false, the statement will not be executed and the the program will move on. Here is an example: Inports System Module Module1 Sub Main() Dim Answer As Char Do Console.Write("Are we there yet (1=Yes/0=No)? ") Answer = Console.ReadLine() Loop While Answer <> "1" Console.WriteLine("Wonderful, we have arrived") Console.WriteLine() End Sub End Module Here is an example of running the program: Are we there yet (1=Yes/0=No)? 2 Are we there yet (1=Yes/0=No)? g Are we there yet (1=Yes/0=No)? 7 Are we there yet (1=Yes/0=No)? 3 Are we there yet (1=Yes/0=No)? k Are we there yet (1=Yes/0=No)? 1 Wonderful, we have arrived As you may guess already, the Condition must provide a way for it to be true and to be false. Otherwise, the looping would be executed over and over again.

Practical Learning: Using do...While

The Do...Loop Until Statement

An alternative to the Do... Loop While uses the following formula:

Do
    Statement(s)
Loop Until Condition

Once again, the Statement(s) section executes first. After executing the Statement(s), the compiler checks the Condition. If the Condition is true, the compiler returns to the Statement(s) section to execute it. This will continue until the Condition is false. Once the Condition becomes false, the compiler gets out of this loop and continues with the section under the Loop Until line.

Here is an example:

Imports System

Module Module1

    Sub Main()
        Dim Answer As Char

        Do
            Console.Write("Are we there yet (1=Yes/0=No)? ")
            Answer = Console.ReadLine()
        Loop Until Answer = "1"

        Console.WriteLine("Wonderful, we have arrived")
        Console.WriteLine()
    End Sub

End Module

The Do While... Loop Statement

As mentioned above, the Do While... Loop expression executes a statement first before checking a condition that would allow it to repeat. If you want to check a condition first before executing a statement, you can use another version as Do While... Loop. Its formula is:

Do While Condition
  Statement(s)
Loop

In this case, the compiler checks the Condition first. If the Condition is true, the compiler then executes the Statement(s) and checks the Condition again. If the Condition is false, or when the Condition becomes false, the compiler skips the Statement(s) section and continues the code below the Loop keyword.

Here is an example:

Inports System

Module Module1

    Sub Main()
        Dim Number As Short

        Do While Number < 46
            Console.Write("{0} ", Number)
            Number += 4
        Loop

        Console.WriteLine()
        Console.WriteLine("Counting Stopped at: {0}", Number)
        Console.WriteLine()
    End Sub

End Module

This would produce:

0 4 8 12 16 20 24 28 32 36 40 44
Counting Stopped at: 48

The Do Until... Loop Statement

An alternative to the Do While... Loop loop uses the following formula:

Do Until Condition
    Statement(s)
Loop

This loop works like the Do While... Loop expression. The compiler examines the Condition first. If the condition is true, then it executes the Statement(s) section.

Here is an example:

Inports System

Module Module1

    Sub Main()
        Dim Answer As Char

        Do Until (Answer = "1")
            Console.Write("Are we there yet (1=Yes/0=No)? ")
            Answer = Console.ReadLine()
        Loop

        Console.WriteLine("Wonderful, we have arrived")
        Console.WriteLine()
    End Sub

End Module

Loop Counters

Introduction

The looping statements we reviewed above are used when you don't know or can't anticipate the number of times a condition needs to be checked in order to execute a statement. If you know with certainty how many times you want to execute a statement, you can use another form of loops that use the For...Next expression.

The For...To...Next Loop

 One of the loop counters you can use is For...To...Next. Its formula is:

For Counter = Start To End
  Statement(s)
Next

Used for counting, the expression begins counting at the Start point. Then it examines whether the current value (after starting to count) is lower than End. If that's the case, it then executes the Statement(s). Next, it increments the value of Counter by 1 and examines the condition again. This process goes on until the value of Counter becomes equal to the End value. Once this condition is reached, the looping stops.

Here is an example:

Inports System

Module Module1

    Sub Main()
        Dim Number As Short

        For Number = 5 To 16
            Console.Write("{0} ", Number)
        Next

        Console.WriteLine()
        Console.WriteLine("Counting Stopped at: {0}", Number)
        Console.WriteLine()
    End Sub

End Module

This would produce:

5 6 7 8 9 10 11 12 13 14 15 16
Counting Stopped at: 17

Stepping the Counting Loop

The formula above will increment the counting by 1 at the end of each statement. If you want to control how the incrementing processes, you can set your own, using the Step option. Here is the formula:

For Counter = Start To End Step Increment
  Statement(s)
Next

You can set the incrementing value to your choice. If the value of Increment is positive, the Counter will be added its value. Here is an example:

Inports System

Module Module1

    Sub Main()
        Dim Number As Short

        For Number = 5 To 42 Step 4
            Console.Write("{0} ", Number)
        Next

        Console.WriteLine()
    End Sub

End Module

This would produce:

5 9 13 17 21 25 29 33 37 41

You can also set a negative value to the Increment factor, in which case the Counter will be subtracted the set value.

Techniques of Writing Conditional Statements

Conditional Nesting

A condition can be created inside of another to write a more effective statement. This is referred to as nesting one condition inside of another. Almost any condition can be part of another and multiple conditions can be included inside of others.

As we have learned, different conditional statements are applied in specific circumstances. In some situations, they are interchangeable or one can be applied just like another, which becomes a matter of choice. Statements can be combined to render a better result with each playing an appropriate role.

Here is an example of an if condition nested inside of a do...while loop:

Imports System

Module Module1

    Sub Main()
        Dim SittingDown As Char
        Dim SitDown As String

        Do
            Console.Write("Are you sitting down now(y/n)? ")
            SitDown = Console.ReadLine()
            SittingDown = CChar(SitDown)

            If SittingDown <> "y" Then
                Console.WriteLine("Could you please sit down for the next exercise? ")
            End If
        Loop While Not (SittingDown = "y")

        Console.WriteLine()
    End Sub

End Module

Here is an example of running the program:

Are you sitting down now(y/n)? n
Could you please sit down for the next exercise?
Are you sitting down now(y/n)? a
Could you please sit down for the next exercise?
Are you sitting down now(y/n)? k
Could you please sit down for the next exercise?
Are you sitting down now(y/n)? y

One of the reasons you would need to nest conditions is because one would lead to another. Sometimes, before checking one condition, another primary condition would have to be met. Our ergonomic program asks the user whether she is sitting down. Once the user is sitting down, you would write an exercise she would perform. Depending on her strength, at a certain time, one user will be tired and want to stop while for the same amount of previous exercises, another user would like to continue. Before continuing with a subsequent exercise, you may want to check whether the user would like to continue. Of course, this would be easily done with:

If the user answers No, you can stop the program. If she answers Yes, you would need to continue the program with another exercise. Because the user answered Yes, the subsequent exercise would be included in the previous condition because it does not apply for a user who wants to stop. In this case, one “if” could be inserted inside of another. Here is an example:

Practical Learning: Nesting Conditions

Exiting Sub

Imagine you are in the middle of a Main procedure (or another of the procedure we will learn to create in the new few lessons). If a certain condition is met, you may need to get out of the procedure to condition the application (out of the current procedure). To do this, the Visual Basic language provides the Exit Sub expression. To use it, you simply type Exit Sub once the undesired condition is met. Consider the following example:

Imports System

Module Module1

    Sub Main()
        Dim i As Integer

        For i = 5 To 18 Step 1
            If i = 12 Then
                Exit Sub
            End If
            Console.WriteLine("Value: {0}", i)
        Next
    End Sub

End Module

In this case, the compiler starts counting at 5 and displays the corresponding value on the console. If the counter reaches 12, it gets out of Main, which causes it to stop. Therefore, this would produce:

Value: 5
Value: 6
Value: 7
Value: 8
Value: 9
Value: 10
Value: 11

The Goto Statement

The Goto statement allows a program execution to jump to another section of a procedure in which it is being used. In order to use the Goto statement, insert a name on a particular section of your procedure so you can refer to that name. The name, also called a label, is made of one word and follows the rules we have learned about names (the name can be anything), then followed by a colon ":".

The following program uses a for loop to count from 2 to 18, but when it encounters 10, it jumps to a designated section of the program:

In the same way, you can create as many labels as you judge them necessary in your code and refer to them when you want. Here is an example with two labels:

Imports System

Module Module1

    Sub Main()
        Dim Answer As Byte

        Console.WriteLine(" -=- Multiple Choice Question -=-")
        Console.WriteLine("To create a constant in your code, you can use the Constant keyword")
        Console.Write("Your choice (1=True/2=False)? ")
        Answer = Console.ReadLine()

        If Answer = 1 Then GoTo Wrong
        If Answer = 2 Then GoTo Right

Wrong:  Console.WriteLine(vbCrLf & "Wrong: The keyword used to create a constant is Const")
        Exit Sub

Right:  Console.WriteLine(vbCrLf & "Right: Constant is not a keyword")

    End Sub

End Module

Here is an example of executing the program with Answer = 1:

-=- Multiple Choice Question -=-
To create a constant in your code, you can use the Constant keyword
Your choice (1=True/2=False)? 1

Wrong: The keyword used to create a constant is Const

Here is another example of executing the same program with Answer = 2:

-=- Multiple Choice Question -=-
To create a constant in your code, you can use the Constant keyword
Your choice (1=True/2=False)? 2

Right: Constant is not a keyword

Conditional Conjunctions and Disjunctions

Introduction

A logical operation is one that is performed on one or two expressions to check the truthfulness or falsity. The comparison is performed using one of three special keywords Not, And, or Or.

Logical Not

When a variable is declared and receives a value (this could be done through initialization or a change of value) in a program, it becomes alive. When a variable is not being used or is not available for processing (in visual programming, it would be considered as disabled) to make a variable (temporarily) unusable, you can nullify its value. To render a variable unavailable during the evolution of a program, apply the logical not operator which is Not. Its syntax is:

Not Value

There are two main ways you can use the logical Not operator. The most classic way of using the logical Not operator is to check the state of a variable.

When a variable holds a value, it is "alive". To make it not available, you can "not" it. When a variable has been "notted", its logical value has changed. If the logical value was True, it would be changed to False and vice versa. Therefore, you can inverse the logical value of a variable by "notting" or not "notting" it.

Here is an example:

Inports System

Module Module1

    Sub Main()
        Dim IsFullTime As Boolean

        Console.WriteLine("Is Employee Full Time? {0}", IsFullTime)

        Console.WriteLine("Is Employee Full Time? {0}", Not IsFullTime)
    End Sub

End Module

This would produce:

Is Employee Full Time? False
Is Employee Full Time? True

Logical Conjunction: And

A logical conjunction is an operation used to check two conditions for absolute truthfulness. This operation uses the And keyword. The formula to use the And operator is

Condition1 And Condition2

The left condition, Condition1, is first checked. If it is False, the whole expression is rendered False and the checking process stopped. If the first condition, Condition1, is True, then the second condition, Condition2, is checked. If the right condition is False, the whole expression is False, even if the first is True. In the same way, if both conditions are false, the whole expression is False. Only if both conditions are True is the whole condition true. This can be resumed as follows:

Here is an example:

Module Module1

    Sub Main()
        Dim SittingDown As Char
        Dim SitDown As String
        Dim WantToContinue As String

        Console.Write("Are you sitting down now(y/n)? ")
        SitDown = Console.ReadLine()
        SittingDown = CChar(SitDown)

        If (SittingDown <> "y") And (SittingDown <> "Y") Then
            Console.WriteLine("Could you please sit down for the next exercise? ")
        End If

        Console.WriteLine()
    End Sub

End Module

Here is one example of running the program:

Are you sitting down now(y/n)? n
Could you please sit down for the next exercise?
Are you sitting down now(y/n)? N
Could you please sit down for the next exercise?
Are you sitting down now(y/n)? d
Could you please sit down for the next exercise?
Are you sitting down now(y/n)? y
Good
We will stop the session now.
Thanks.

Logical Disjunction: OR

A logical disjunction is performed on two conditions for a single truthfulness. This operation uses the Or keyword on the following formula:

Condition1 OR Condition2

 The left condition, Condition1, is first checked. If Condition1 is True, then the whole expression is true, regardless of the outcome of the second. If Condition1 is False, then Condition2 is checked. If Condition2 is True, the whole expression is True even if Condition1 was False. If both conditions are True, the whole expression is True. The whole expression is false only if both Condition1 and Condition2 are False. This can be resumed as follows:

Here is an example:

Module Module1

    Sub Main()
        Dim SittingDown As Char
        Dim SitDown As String
        Dim WantToContinue As String

        Console.Write("Are you sitting down now(y/n)? ")
        SitDown = Console.ReadLine()
        SittingDown = CChar(SitDown)

        If (SittingDown = "n") Or (SittingDown = "N") Then
            Console.WriteLine("Could you please sit down for the next exercise? ")
        End If

        Console.WriteLine()
    End Sub

End Module

Practical Learning: Using Or