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Visual Basic 2008 9.0 .NET Examples and Ebook
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| Suppose we need a program that gives us the sum of 3 entered values. The sum together with the entered values has to be brought to the console.
Something like this : |
| Output : Value 1 ?
10
Value 2 ?
20
Value 3 ?
30
10 + 20 + 30 = 60 |
| Following example is a possible solution. |
| Module Example1
Sub Main()
Dim value1, value2, value3 As Integer
Dim sum As Integer
Console.WriteLine("Value 1 ?")
value1 = Console.ReadLine()
sum += value1
Console.WriteLine("Value 2 ?")
value2 = Console.ReadLine()
sum += value2
Console.WriteLine("Value 3 ?")
value3 = Console.ReadLine()
sum += value3
Console.Write(value1)
Console.Write(" + ")
Console.Write(value2)
Console.Write(" + ")
Console.Write(value3)
Console.Write(" = ")
Console.Write(sum)
Console.ReadLine()
End Sub
End Module
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| An alternative solution could use an array.
An array is a collection of elements of the same type. For instance a collection of Integer elements. |
| Module Example2
Sub Main()
Dim values(2) As Integer
Dim sum As Integer
Console.WriteLine("Value 1 ?")
values(0) = Console.ReadLine()
sum += values(0)
Console.WriteLine("Value 2 ?")
values(1) = Console.ReadLine()
sum += values(1)
Console.WriteLine("Value 3 ?")
values(2) = Console.ReadLine()
sum += values(2)
Console.Write(values(0))
Console.Write(" + ")
Console.Write(values(1))
Console.Write(" + ")
Console.Write(values(2))
Console.Write(" = ")
Console.Write(sum)
Console.ReadLine()
End Sub
End Module
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| Output : Value 1 ?
10
Value 2 ?
20
Value 2 ?
30
10 + 20 + 30 = 60 |
| Every element of an array has an index. This index can be used to address the element. The index of the first element ( also called "lowerbound" ) is always 0, the index of the second element is 1, the index of the third element is 2, ..., the index of the last element ( also called "upperbound" ) is equal to the number of elements minus 1.
For instance an array of 10 elements, has upperbound 9.
To address an element of the array, both the identifier of the array variable and the index of the element are needed. For instance values(2) is a Integer expression resulting in the value of the third element.
All Integer expressions can be used to express the index of the element, for instance values(index) with index being an Integer variable containing 2, would also evaluate to the value of the third element.
values(index + 1) would then evaluate to the value of the fourth element.
Before an array is used, it is usually declared : |
| Dim <identifier>(<upperbound>) <type-specifier>
|
| The element of an array are stored together in memory.
An Integer array with 3 elements, will roughly consume 96 bits ( equal amount as 3 separate Integer variables ).
An advantage of using an array is that one can address the elements of this array in a dynamical fashion. The same expression ( for instance values(index) ) can be used several times at runtime, to address different elements. If index is 0, values(index) addresses the first element, if index is 1, values(index) addresses the second element, ... .
This cannot be done ( or is very hard to do ) when separate variables are used. |
| Module Example3
Sub Main()
Dim values(2) As Integer
Dim sum As Integer
Dim index As Integer
For index = 0 To 2
Console.WriteLine("Value " & index + 1 & " ?")
values(index) = Console.ReadLine()
sum += values(index)
Next
Console.Write(values(0))
For index = 1 To 2
Console.Write(" + ")
Console.Write(values(index))
Next
Console.Write(" = ")
Console.Write(sum)
Console.ReadLine()
End Sub
End Module
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| Output : Value 1 ?
10
Value 2 ?
20
Value 2 ?
30
10 + 20 + 30 = 60 |
| A For ... Next is ideal for performing an operation on all ( or some ) elements of the array.
A countervariable ( starting from the lowerbound, stepping 1 and ending at the upperbound ) can be used to dynamically and iteratively express all indexes of all elements. |
| Module Example4
Sub Main()
Console.WriteLine("Count ?")
Dim count As Integer = Console.ReadLine()
Dim values(count) As Integer
Dim sum As Integer
Dim index As Integer
For index = 0 To count - 1
Console.WriteLine("Value " & index + 1 & " ?")
values(index) = Console.ReadLine()
sum += values(index)
Next
Console.Write(values(0))
For index = 1 To count - 1
Console.Write(" + ")
Console.Write(values(index))
Next
Console.Write(" = ")
Console.Write(sum)
Console.ReadLine()
End Sub
End Module
Download Broncode |
| Output : Value 1 ?
10
Value 2 ?
20
Value 2 ?
30
10 + 20 + 30 = 60 |
| Another advantage of arrays is that the size of the array ( the number of elements ) can be changed at runtime ( see next topic ).
Following examples illustrates how :
- all elements of an array contain the default value of the element type of that array, all elements of values contain 0 after declaration of values, all elements of conditions contain False after declaration of conditions
- a runtime error ( IndexOutOfRangeException ) will be produces when we address an element on a non-existing index |
| Module Example5
Sub Main()
Dim values(4) As Integer
Dim conditions(4) As Boolean
Dim index As Integer
For index = 0 To 4
Console.WriteLine(values(index))
Console.WriteLine(conditions(index))
Next
Console.ReadLine()
End Sub
End Module
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| Output : 0
False
0
False
0
False
0
False
0
False |
Exercises
| Task :
Make a program that fills an array with 5 elements with values entered by the user.
Print out all element in reverse order. |
| Output : Value 1 : 6
Value 2 : 2
Value 3 : 5
Value 4 : 4
Value 5 : 9
Element 5 ( at index 4 ) : 9
Element 4 ( at index 3 ) : 4
Element 3 ( at index 2 ) : 5
Element 2 ( at index 1 ) : 2
Element 1 ( at index 0 ) : 6 |
| Module Exercise1Solution
Sub Main()
Dim count As Integer = 5
Dim upperbound As Integer = count - 1
Dim values(upperbound) As Integer
Dim index As Integer
For index = 0 To upperbound
Console.Write("Value " & (index + 1) & " : ")
values(index) = Console.ReadLine()
Next
For index = upperbound To 0 Step -1
Console.WriteLine("Element " & (index + 1) & _
" ( at index " & (index) & " ) : " & _
values(index))
Next
Console.ReadLine()
End Sub
End Module
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| Make a program that first asks the user how many values to enter. The program will then fill an array with all entered values. When all values are entered the program prints out the highest entered value and its position ( and index ) in the array. |
| Output : Count : 3
Value 1 : -8
Value 2 : -2
Value 3 : -3
Highest Value : -2 ( element 2 at index 1 ) |
| Module Exercise2Solution
Sub Main()
Console.Write("Count : ")
Dim count As Integer = Console.ReadLine()
Dim upperbound As Integer = count - 1
Dim values(upperbound) As Integer
Dim index, highestValueIndex As Integer
For index = 0 To upperbound
Console.Write("Value " & (index + 1) & " : ")
values(index) = Console.ReadLine()
If values(highestValueIndex) < values(index) Then
highestValueIndex = index
End If
Next
Console.WriteLine("Highest Value : " & values(highestValueIndex) & _
" ( element " & (highestValueIndex + 1) & _
" at index " & highestValueIndex & " )")
Console.ReadLine()
End Sub
End Module
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| Make a program that fills an array with 10 elements with values 10 to 1 : |
| index 0 1 2 3 4 5 6 7 8 9
value 10 9 8 7 6 5 4 3 2 1 |
| Only 2 variables may be used in this exercise.
Print out all elements. |
| Output : element 1 ( index 0 ) : 10
element 2 ( index 1 ) : 9
element 3 ( index 2 ) : 8
element 4 ( index 3 ) : 7
element 5 ( index 4 ) : 6
element 6 ( index 5 ) : 5
element 7 ( index 6 ) : 4
element 8 ( index 7 ) : 3
element 9 ( index 8 ) : 2
element 10 ( index 9 ) : 1 |
| Module Exercise3Solution
Sub Main()
Dim values(9) As Integer
Dim index As Integer
For index = 0 To 9
values(index) = 10 - index
Console.WriteLine("element " & (index + 1) & _
" ( index " & index & " ) : " & _
values(index))
Next
Console.ReadLine()
End Sub
End Module
Download Broncode |
| Make a program that fills an array with 10 elements with values 1 to 10 : |
| index 0 1 2 3 4 5 6 7 8 9
value 1 2 3 4 5 6 7 8 9 10 |
| Print out all elements.
Replace all elements until the are in reverse order : |
| index 0 1 2 3 4 5 6 7 8 9
value 10 9 8 7 6 5 4 3 2 1 |
| Output : element 1 ( index 0 ) : 1
element 2 ( index 1 ) : 2
element 3 ( index 2 ) : 3
element 4 ( index 3 ) : 4
element 5 ( index 4 ) : 5
element 6 ( index 5 ) : 6
element 7 ( index 6 ) : 7
element 8 ( index 7 ) : 8
element 9 ( index 8 ) : 9
element 10 ( index 9 ) : 10
element 1 ( index 0 ) : 10
element 2 ( index 1 ) : 9
element 3 ( index 2 ) : 8
element 4 ( index 3 ) : 7
element 5 ( index 4 ) : 6
element 6 ( index 5 ) : 5
element 7 ( index 6 ) : 4
element 8 ( index 7 ) : 3
element 9 ( index 8 ) : 2
element 10 ( index 9 ) : 1 |
| Module Exercise4Solution
Sub Main()
Dim count As Integer = 10
Dim upperbound As Integer = count - 1
Dim values(upperbound) As Integer
Dim index As Integer
For index = 0 To upperbound
values(index) = index + 1
Next
For index = 0 To upperbound
Console.WriteLine("element " & (index + 1) & _
" ( index " & index & " ) : " & _
values(index))
Next
Console.WriteLine()
Dim backup As Integer
For index = 0 To (count \ 2) - 1
backup = values(index)
values(index) = values(upperbound - index)
values(upperbound - index) = backup
Next
For index = 0 To upperbound
Console.WriteLine("element " & (index + 1) & _
" ( index " & index & " ) : " & _
values(index))
Next
Console.ReadLine()
End Sub
End Module
Download Broncode |
| Make a program that fills an array with 10 elements with values 1 to 10 : |
| index 0 1 2 3 4 5 6 7 8 9
value 1 2 3 4 5 6 7 8 9 10 |
| Print out all elements.
Shift all elements one position to the left : |
| index 0 1 2 3 4 5 6 7 8 9
value 2 3 4 5 6 7 8 9 10 1 |
| Output : element 1 ( index 0 ) : 1
element 2 ( index 1 ) : 2
element 3 ( index 2 ) : 3
element 4 ( index 3 ) : 4
element 5 ( index 4 ) : 5
element 6 ( index 5 ) : 6
element 7 ( index 6 ) : 7
element 8 ( index 7 ) : 8
element 9 ( index 8 ) : 9
element 10 ( index 9 ) : 10
element 1 ( index 0 ) : 2
element 2 ( index 1 ) : 3
element 3 ( index 2 ) : 4
element 4 ( index 3 ) : 5
element 5 ( index 4 ) : 6
element 6 ( index 5 ) : 7
element 7 ( index 6 ) : 8
element 8 ( index 7 ) : 9
element 9 ( index 8 ) : 10
element 10 ( index 9 ) : 1 |
| Module Exercise5Solution
Sub Main()
Dim count As Integer = 10
Dim upperbound As Integer = count - 1
Dim values(upperbound) As Integer
Dim index As Integer
For index = 0 To upperbound
values(index) = index + 1
Next
For index = 0 To upperbound
Console.WriteLine("element " & (index + 1) & _
" ( index " & index & " ) : " & _
values(index))
Next
Console.WriteLine()
Dim backup As Integer = values(0)
For index = 0 To (upperbound - 1)
values(index) = values(index + 1)
Next
values(upperbound) = backup
For index = 0 To upperbound
Console.WriteLine("element " & (index + 1) & _
" ( index " & index & " ) : " & _
values(index))
Next
Console.ReadLine()
End Sub
End Module
Download Broncode |
| Make a program that fills an array with 10 elements with values 1 to 10 : |
| array 1 :
index 0 1 2 3 4 5 6 7 8 9
value 1 2 3 4 5 6 7 8 9 10 |
| Print out all elements.
Create a second array filled with values 10 to 1 : |
| array 2 :
index 0 1 2 3 4 5 6 7 8 9
value 10 9 8 7 6 5 4 3 2 1 |
| Print out all elements of this second array.
Create a third array and fill it with the highest of the two values of the elements of the first and second arrays at corresponding positions. |
| array 3 :
index 0 1 2 3 4 5 6 7 8 9
value 10 9 8 7 6 6 7 8 9 10 |
| Print out all elements of this third array. |
| Output : Array 1 :
element 1 ( index 0 ) : 1
element 2 ( index 1 ) : 2
element 3 ( index 2 ) : 3
element 4 ( index 3 ) : 4
element 5 ( index 4 ) : 5
element 6 ( index 5 ) : 6
element 7 ( index 6 ) : 7
element 8 ( index 7 ) : 8
element 9 ( index 8 ) : 9
element 10 ( index 9 ) : 10
Array 2 :
element 1 ( index 0 ) : 10
element 2 ( index 1 ) : 9
element 3 ( index 2 ) : 8
element 4 ( index 3 ) : 7
element 5 ( index 4 ) : 6
element 6 ( index 5 ) : 5
element 7 ( index 6 ) : 4
element 8 ( index 7 ) : 3
element 9 ( index 8 ) : 2
element 10 ( index 9 ) : 1
Array 3 :
element 1 ( index 0 ) : 10
element 2 ( index 1 ) : 9
element 3 ( index 2 ) : 8
element 4 ( index 3 ) : 7
element 5 ( index 4 ) : 6
element 6 ( index 5 ) : 6
element 7 ( index 6 ) : 7
element 8 ( index 7 ) : 8
element 9 ( index 8 ) : 9
element 10 ( index 9 ) : 10 |
| Module Exercise6Solution
Sub Main()
Dim count As Integer = 10
Dim upperbound As Integer = count - 1
Dim values1(upperbound) As Integer
Dim values2(upperbound) As Integer
Dim values3(upperbound) As Integer
Dim index As Integer
For index = 0 To upperbound
values1(index) = index + 1
Next
Console.WriteLine("Array 1 :")
For index = 0 To upperbound
Console.WriteLine("element " & (index + 1) & _
" ( index " & index & " ) : " & _
values1(index))
Next
Console.WriteLine()
For index = 0 To upperbound
values2(index) = count - index
Next
Console.WriteLine("Array 2 :")
For index = 0 To upperbound
Console.WriteLine("element " & (index + 1) & _
" ( index " & index & " ) : " & _
values2(index))
Next
Console.WriteLine()
For index = 0 To upperbound
If values1(index) >= values2(index) Then
values3(index) = values1(index)
Else
values3(index) = values2(index)
End If
Next
Console.WriteLine("Array 3 :")
For index = 0 To upperbound
Console.WriteLine("element " & (index + 1) & _
" ( index " & index & " ) : " & _
values3(index))
Next
Console.WriteLine()
Console.ReadLine()
End Sub
End Module
Download Broncode |
| Create a program that fills an array with Fibonacci numbers.
Fibonacci : 1 1 2 3 5 8 13 21 34 55 89 ...
The first two values are 1, all next values are the sum of the previous two. |
| Output : Count : 11
1 1 2 3 5 8 13 21 34 55 89 |
| Module Exercise7Solution
Sub Main()
Console.Write("Count : ")
Dim count As Integer = Console.ReadLine()
If count <= 0 Then
Console.WriteLine("Error : Minimum count 1.")
Else
Dim upperbound As Integer = count - 1
Dim fibonacci(upperbound) As Integer
Dim index As Integer
fibonacci(0) = 1
If count > 1 Then
fibonacci(1) = 1
For index = 2 To upperbound
fibonacci(index) = fibonacci(index - 1) + fibonacci(index - 2)
Next
End If
For index = 0 To upperbound
Console.Write(fibonacci(index) & " ")
Next
End If
Console.ReadLine()
End Sub
End Module
Download Broncode |
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