1. Arrays 1

2. Outline
Introduction Arrays Declaring and Allocating Arrays Examples Using Arrays   Allocating an Array   Initializing the Values in an Array   Summing the Elements of an Array   Using Arrays to Analyze Survey Results Using Histograms to Display Array Data Graphically Passing Arrays to Procedures Sorting Array
Searching Arrays

3. Introduction
Arrays
Arrays are data structures consisting of data items of the same type.
“Static” entities:
They remain the same size once they are created
Position number:
Values that indicate specific locations within arrays
The first element in every array is the zeroth element

4. Arrays
Name of array (note that all elements of this array have the same name, numberArray)
numberArray(0)
-45
numberArray(1) 6
numberArray(2)
numberArray(3) 72
numberArray(4)
1543
numberArray(5)
-89
numberArray(6)
numberArray(7) 62
numberArray(8) -3
Position number (index or subscript) of the element within array numberArray
numberArray(9) 1
numberArray(10)
6453
numberArray(11) 78
Fig. 7.1 Array consisting of 12 elements.

5. Arrays numberArray.Length ‘ 12 numberArray.GetUpperBound(0) ‘11
All arrays have access to the methods and properties of class System.Array, including:
Length property
numberArray.Length ‘ 12
GetUpperBound method
Returns the index of the last element in the array
The value returned by this GetUpperBound is one less than the value of the array’s Length property
numberArray.GetUpperBound(0) ‘11

6. Declaring and Allocating Arrays
Memory
The amount of memory required by an array depends on the length of the array and the size of the data type of the elements in the array
The declaration of an array creates a variable that can store a reference to an array but does not create the array in memory.
To declare an array, the programmer provides the array’s name and data type. The following statement declares numberArray.
Dim numberArray As Integer()
The parentheses that follow
the data type indicate that
numberArray is an array.

7. Declaring and Allocating Arrays
Before the array can be used, the programmer must specify the size of the array and allocate memory for the array, using Keyword New:
‘ Declaration
Dim numberArray As Integer()
‘ Allocation
numberArray = New Integer(11) {}
Array bounds : Determine what indices can be used to access an element in the array. Here ( 0 – 11)

8. Declaring and Allocating Arrays
numberArray = New Integer(11) { }
The braces ({ and }) are called an initializer list and specify the initial values of the elements in the array.
When the initializer list is empty, the elements in the array are initialized to the default value for the data type of the elements of the array.
The default value is 0 for numeric primitive data-type variables, False for Boolean variables and Nothing for references.

9. Declaring and Allocating Arrays
Visual Basic can determine the array bounds from the number of elements in the initializer list.
Thus, it is not necessary to specify the size of the array when a non-empty initializer list is present.
Examples:
Dim numbers As Integer()
numbers = New Integer() {1, 2, 3, 6} ‘initialization
Dim numberArray As Integer() = New Integer(11) {}
Dim array1, array2 As Double()

10. Declaring and Allocating Arrays
How can we set up a Non-Fixed size array?
First set up an array with empty brackets
Dim numbers( 10) As Integer
We can then use other value to reset the array. You reset an array by using the ReDim word.
You then specify the new value. Like this:
ReDim numbers(20)

11. Examples Using Arrays Several examples that demonstrate Declaration
Allocation
Initialization of arrays

12. Allocate an array of 10 Integer elements,
1 ' Fig. 7.2: CreateArray.vb
2 ' Declaring and allocating an array. 3
4 Imports System.Windows.Forms 5
6 Module modCreateArray 7
Sub Main()
Dim output As String
Dim i As Integer 11
Dim array As Integer() ' declare array variable
array = New Integer(9) {} ' allocate memory for array 14
output &= "Subscript " & vbTab & "Value" & vbCrLf 16
' display values in array
For i = 0 To array.GetUpperBound(0)
output &= i & vbTab & array(i) & vbCrLf
Next 21
output &= vbCrLf & "The array contains " & _
array.Length & " elements." 24
MessageBox.Show(output, "Array of Integer Values", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main 28
29 End Module ' modCreateArray
Allocate an array of 10 Integer elements,
which are initially zero. The program displays the array elements in tabular format in a dialog.
Allocate an array of 10 elements using New and assigns it to array
Appends to output the headings for the columns displayed by the program

13. Examples Using Arrays

14. 1 ' Fig. 7.3: InitArray.vb
2 ' Initializing arrays. 3
4 Imports System.Windows.Forms 5
6 Module modInitArray 7
Sub Main()
Dim output As String
Dim i As Integer 11
Dim array1, array2 As Integer() ' declare two arrays 13
' initializer list specifies number of elements
' and value of each element
array1 = New Integer() {32, 27, 64, 18, 95, _
, 90, 70, 60, 37} 18
' allocate array2 based on length of array1
array2 = New Integer(array1.GetUpperBound(0)) {} 21
' set values in array2 by a calculation
For i = 0 To array2.GetUpperBound(0)
array2(i) = * i
Next
Creates two integer arrays of 10 elements each and sets the values of the elements, using an initializer list and a For structure.
One statement is used to declare the two arrays
Allocates the 10 elements of array1 with New and initialize the values in the array, using an initializer list
Allocates array2, whose size is determined by arry1.GetUpperBound(0), so that array1 and array2 have the same upper bound
Initializes each element in array2 to the even integers

15. Uses the values in the arrays to build String output, which is displayed in a MessageBox26
output &= "Subscript " & vbTab & "Array1" & vbTab & _
"Array2" & vbCrLf 29
' display values for both arrays
For i = 0 To array1.GetUpperBound(0)
output &= i & vbTab & array1(i) & vbTab & array2(i) & _
vbCrLf
Next 35
MessageBox.Show(output, "Array of Integer Values", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main 39
40 End Module ' modInitArray

16. Declares, allocates and initializes the 10-element array, array
1 ' Fig. 7.4: SumArray.vb
2 ' Computing sum of elements in array. 3
4 Imports System.Windows.Forms 5
6 Module modSumArray 7
Sub Main()
Dim array As Integer() = New Integer() _
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10} 11
Dim total As Integer = 0, i As Integer = 0 13
' sum array element values
For i = 0 To array.GetUpperBound(0)
total += array(i)
Next 18
MessageBox.Show("Total of array elements: " & total, _
"Sum the elements of an Array", MessageBoxButtons.OK, _
MessageBoxIcon.Information)
End Sub ' Main 23
24 End Module ' modSumArray
Sums the values contained in a
10-element integer array.
Declares, allocates and initializes the 10-element array, array

17. 1 ' Fig. 7.6: Histogram.vb
2 ' Using data to create histograms.
4 Imports System.Windows.Forms
5 Module modHistogram
7 Sub Main()
Dim output As String ' output string
Dim i, j As Integer ' counters 11
' create data array
Dim array1 As Integer() = New Integer() _
{19, 3, 15, 7, 11, 9, 13, 5, 17, 1} 15
output &= "Element " & vbTab & "Value " & vbTab & _
"Histogram" 18
For i = 0 To array1.GetUpperBound(0)
output &= vbCrLf & i & vbTab & array1(i) & vbTab 21
For j = 1 To array1(i)
output &= "*" ' add one asterisk
Next 25
Next 27
MessageBox.show(output, "Histogram Printing Program", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub ' Main 31
32 End Module ' modHistogram
Nested For loops append the bars to the String that is displayed in the MessageBox
Inner For structure counts from 1 to array(i), which is the value in the ith index of array1

19. Array of Controls
We can define an array of controls, using the same statements used to declare a variable array. For example, to declare an array of 20 buttons, use:
Dim btnArray As Button() = New Button(20) { }

20. Array of Controls
Say we have 10 check boxes (chkBox01, chkBox02, chkBox03, chkBox04, chkBox05, chkBox06, chkBox07, chkBox08, chkBox09, chkBox10) on a form and we need to examine each check box’s Checked property. If that property is True, we need to process 30 lines of additional code.
For one check box, that code would be:
If chkBox01.Checked Then
[do these 30 lines of code]
End If
We would need to repeat this 9 more times (for the nine remaining check boxes), yielding a total of 32 x 10 = 320 lines of code.

21. Array of Controls
Here’s the solution. Define an array of 10 check box controls and assign the array values to existing controls:
Dim MyCheck As CheckBox() = new CheckBox(10) { }
MyCheck(1) = chkBox01
MyCheck(2) = chkBox02
MyCheck(3) = chkBox03
MyCheck(4) = chkBox04
MyCheck(5) = chkBox05
MyCheck(6) = chkBox06
MyCheck(7) = chkBox07
MyCheck(8) = chkBox08
MyCheck(9) = chkBox09
MyCheck(10) = chkBox10
Dim I As Integer .
For I = 1 To 10
If MyCheck(I).Checked Then
[do these 30 lines of code]
End If
Next I

22. Array of Controls
The 320 lines of code have been reduced to about 45 (including all the declarations) and code maintenance is now much easier.
Obviously, it is not necessary to use control arrays, but they do have their advantages.