Visual Basic 2008 9.0 .NET Examples and Ebook

Suppose we need to bring to the console whether an entered value is "Zero.", "More than zero." or "Less than zero.".

We know that based on a condition of an If-statement we can let our algorithm decide between two options. What to do when the condition is true, and what to do when the condition is false.

But in this case, we have more than two options, we have three options. So we're going to need at least two conditions to make it possible for our algorithm to decide what option to take.

Module Example1
    Sub Main()
        Console.WriteLine("Value ?")
        Dim value As Integer = Console.ReadLine()
        '
        If value = 0 Then
            Console.WriteLine("Zero.")
        Else
            If value > 0 Then
                Console.WriteLine("Above zero.")
            Else
                Console.WriteLine("Bellow zero.")
            End If
        End If
        '
        Console.ReadLine()
    End Sub
End Module

Output :

 Value ?
 <i>0</i>
 Zero.

Output :

 Value ?
 <i>5</i>
 Above zero.

Output :

 Value ?
 <i>-5</i>
 Bellow zero.

The above example illustrates how a decision ( a selection ) can be selected.

Suppose we need to print out the multiplication tables of one to nine.

Output :

 1 x 1 = 1
 1 x 2 = 2
 ...
 1 x 9 = 9
 2 x 1 = 1
 ...
 9 x 9 = 81

Obviously iterations are needed. Almost identical lines follow each other.

What is being iterated here? Some base value ( starting with one and ending with nine ) is being multiplied with all factors from one to nice.

We can start with an iteration that prints out all numbers from one to nine.

Module Example2
    Sub Main()
        Dim baseValue As Integer = 1
        '
        Do While baseValue < 10
            Console.WriteLine(baseValue)
            baseValue = baseValue + 1
        Loop
        '
        Console.ReadLine()
    End Sub
End Module

Output :

 1
 2
 3
 4
 5
 6
 7
 8
 9

In stead of just printing out these numbers, each number should be multiplied with all factors from one to nine.

Lets write an algorithm to print out all multiplications ( with all factors ) of a certain basevalue.

Module Example3
    Sub Main()
        Dim baseValue As Integer = 5
        Dim factor As Integer = 1
        Dim multiplication As Integer
        '
        Do While factor < 10
            multiplication = baseValue * factor
            Console.WriteLine(baseValue & " x " & factor & " = " & _
                              multiplication)
            factor = factor + 1
        Loop
        '
        Console.ReadLine()
    End Sub
End Module

Output :

 5 x 1 = 5
 5 x 2 = 10
 5 x 3 = 15
 5 x 4 = 20
 5 x 5 = 25
 5 x 6 = 30
 5 x 7 = 35
 5 x 8 = 40
 5 x 9 = 45

Now we only need to integrate both above algorithms.

Module Example4
    Sub Main()
        Dim baseValue As Integer = 1
        Dim factor As Integer = 1
        Dim multiplication As Integer
        '
        Do While baseValue < 10
            Do While factor < 10
                multiplication = baseValue * factor
                Console.WriteLine(baseValue & " x " & factor & " = " & _
                                  multiplication)
                factor = factor + 1
            Loop
            baseValue = baseValue + 1
        Loop
        '
        Console.ReadLine()
    End Sub
End Module

Output :

 1 x 1 = 1
 1 x 2 = 2
 1 x 3 = 3
 1 x 4 = 4
 1 x 5 = 5
 1 x 6 = 6
 1 x 7 = 7
 1 x 8 = 8
 1 x 9 = 9

In the above solution the iteration Do While factor < 10 ( which gives a table for a certain basevalue ) is repeated for each basevalue ( Do While baseValue < 10 ).

Notice that the output only contains the table for basevalue 1, and not for all following basevalues.

When we add the line factor = 1 at the end ( or beginning ) of iteration factor = 1 this problem is solved.

Module Example5
    Sub Main()
        Dim baseValue As Integer = 1
        Dim factor As Integer = 1
        Dim multiplication As Integer
        '
        Do While baseValue < 10
            Do While factor < 10
                multiplication = baseValue * factor
                Console.WriteLine(baseValue & " x " & factor & " = " & _
                                  multiplication)
                factor = factor + 1
            Loop
            baseValue = baseValue + 1
            factor = 1
        Loop
        '
        Console.ReadLine()
    End Sub
End Module

Output :

 1 x 1 = 1
 1 x 2 = 2
 ...
 1 x 9 = 9
 2 x 1 = 1
 ...
 9 x 9 = 81

As the above example illustrates an iteration can be iterated.

Iterations can be iterated, selections can be selected. And of course, iterations be selected or selections can be iterated.

Suppose we need to print out for all numbers from one to ten if they are even or odd.

Output :

 1 is odd.
 2 is even.
 3 is odd.
 4 is even.
 5 is odd.
 6 is even.
 7 is odd.
 8 is even.
 9 is odd.
 10 is even.

A decision have to be taken by our algorithm to selected whether to print out "even" or to print out "odd". This decision then has to iterated for all numbers starting with one up to nine.

It's easy to start with an algorithm that print out if a certain value is odd or even.

Module Example6
    Sub Main()
        Dim value As Integer = 5
        '
        If value Mod 2 = 0 Then
            Console.WriteLine(value & " is even.")
        Else
            Console.WriteLine(value & " is odd.")
        End If
        '
        Console.ReadLine()
    End Sub
End Module

Output :

 5 is odd.

This decision has to be iterated for all numbers starting with one up to nine.

Module Example7
    Sub Main()
        Dim value As Integer
        '
        Do While value < 10
            value = value + 1
            If value Mod 2 = 0 Then
                Console.WriteLine(value & " is an even number")
            Else
                Console.WriteLine(value & " is an odd number")
            End If
        Loop
        '
        Console.ReadLine()
    End Sub
End Module

Output :

 1 is odd.
 2 is even.
 3 is odd.
 4 is even.
 5 is odd.
 6 is even.
 7 is odd.
 8 is even.
 9 is odd.
 10 is even.

As the above example illustrates a selection can be iterated.

By using sequentially defined instruction, iterations and decisions, the most complex algorithms can be formed.

Task :

Make a program that repeatedly asks for a number. When a value less than zero is entered, the highest entered number is brought on the console.

Output :

 Value ?
 <i>3</i>
 Value ?
 <i>8</i>
 Value ?
 <i>4</i>
 Value ?
 <i>-1</i>
 Highest Value : 8

Solution :

Module Exercise1Solution
    Sub Main()
        Dim value As Integer
        Dim highestValue As Integer
        '
        Do While value >= 0
            Console.WriteLine("Value ?")
            value = Console.ReadLine()
            '
            If value > highestValue Then
                highestValue = value
            End If
        Loop
        '
        Console.WriteLine("Highest Value : " & highestValue)
        '
        Console.ReadLine()
    End Sub
End Module

Task :

Make a program that prints out all numbers ( from small to big ) between two values entered by the user.

Output :

 Value ?
 <i>-4</i>
 Value ?
 <i>3</i>
 Row :
 -3
 -2
 -1
 0
 1
 2

Output :

 Value ?
 <i>2</i>
 Value ?
 <i>2</i>
 Row :

Output :

 Value ?
 <i>2</i>
 Value ?
 <i>-1</i>
 Row :
 0
 1

Output :

 Value ?
 <i>2</i>
 Value ?
 <i>3</i>
 Row :

Solution :

Module Exercise2Solution
    Sub Main()
        Dim value1, value2 As Integer
        Dim smallestValue, highestValue As Integer
        '
        Console.WriteLine("Value ?")
        value1 = Console.ReadLine()
        Console.WriteLine("Value ?")
        value2 = Console.ReadLine()
        '
        If value1 > value2 Then
            highestValue = value1
            smallestValue = value2
        Else
            highestValue = value2
            smallestValue = value1
        End If
        '
        Console.WriteLine("Row :")
        Do While smallestValue + 1 < highestValue
            Console.WriteLine(smallestValue + 1)
            smallestValue = smallestValue + 1
        Loop
        '
        Console.ReadLine()
    End Sub
End Module

Task :

Make a program that accepts a positive numeric value ( not zero ).
When the value is even, the value is divided by 2 and printed out.
When the value is odd, the value is multiplied by 3, added with 1 and printed out.
Repeat this until the value is 1.

Output :

 Value ?
 <i>10</i>
 Row :
 10
 5
 16
 8
 4
 2
 1

Solution :

Module Exercise3Solution
    Sub Main()
        Console.WriteLine("Value ?")
        Dim value As Integer = Console.ReadLine()
        '
        Console.WriteLine("Row : ")
        Do While value <> 1
            Console.WriteLine(value)
            '
            If value Mod 2 = 0 Then
                value = value / 2
            Else
                value = value * 3 + 1
            End If
        Loop
        Console.WriteLine(value)
        '
        Console.ReadLine()
    End Sub
End Module