Display the summary in the text box For ctr = 0 To value - 1
If txtsummary.Text = Then If LCasearrRemarksctr = fail Then
txtsummary.Text = arrNamectr has failed _ in
exams vbCrLf
Else txtsummary.Text = arrNamectr s performance is_
arrRemarksctr vbCrLf End If
Else If LCasearrRemarksctr = fail Then
txtsummary.Text = txtsummary.Text arrNamectr _ has failed in exams vbCrLf
Else txtsummary.Text = txtsummary.Text arrNamectr _
s performance is arrRemarksctr _ vbCrLf End If
End If Next
5.5 Arrays
Till now we have been using variable to store values. We might come across a situation when we might need to store multiple values of similar type. Such as names of 100
students in a school. One way to do it is to declare 100 variables and store all the names. A much more simple and efficient way of storing these variable is using Arrays. An
Array is a memory location that is used to store multiple values. All the values in an array are of the same type, such as Integer or String and are
referenced by their index or subscript number, which is the order in which these values are stored in the array. These values are called the elements of the array.
The number of elements that an array contains is called the length of the array.
In VB.Net all arrays are inherited from the System.Array Class. Arrays can be single or multidimensional. You can determine the dimensions of an array
by the number of subscripts that are used to identify the position of any array element.
A single dimensional array is identified by only a single subscript and an element in a two-dimensional array is identified by two subscripts.
The dimension has to be declared before using them in a program. The array declaration comprises the name of the array and the number of elements the array can contain.
The Syntax of single dimension array is as follows.
Dim ArrayName number of elements as Element Data type. e.g.
Dim studentname10 as string Or
Dim studentname as string = new string10 You can assign the values at runtime or even at the design time.
Design time declaration: Studentname0=”Rohan”
Studentname1=”Mohan” …..
Studentname10=”Nitin”
All arrays starts with the index of 0 i.e. All arrays are Zero Based and there is no provision of an option Base Statement where in you can specify the Lower Bound . This
implies that above array can store 11 elements. Here 0, is the starting index or the lower bound of the array. The lower bound is fixed for all the arrays.
Example 1.
We will create a VB.Net application that will accept the names of students in an single dimension array and display it back.
Add a textbox and set the name property to txtnames. Set the multilane property of the text box to true.
Put a button and write the following in the onclick event.
txtnames.Text = Dim value, count As Integer
Accept how many students names to enter value = CIntInputBoxEnter the number of students name to enter:
Dim arrnamesvalue As String Dim cnt As Integer
For cnt = 0 To value
arrnamescnt = InputBoxEnter the name of student cnt + 1 :, Student Name
Next Display the entered value to the text box
For cnt = 0 To value
If txtnames.Text = Then txtnames.Text = arrnamescnt vbCrLf for carriage returns
Else txtnames.Text = txtnames.Text arrnamescnt vbCrLf
End If Next
Above example will accept number of names to be entered and will add the names in a loop and then redisplay it in a text box.
The Syntax for multi-dimension arrays is as follows: Previously we saw how we can store multiple names of students. But, if we want to store
related data of students like first name, middle name, last name. In such situations you can use multi dimension arrays, such as two-or-three dimension arrays.
Dim ArrayName number of 1
st
element, number of 2
nd
element,…. as element data
type. Or
Simpler form would be
Dim ArrayName number of rows, number of columns as element data type of two dimension.
e.g. Dim studentdetails10,2 as string
Index positions of array elements.
0,0 0,1 1,0 1,1
2,0 2,1 3,0 3,1
… 10,0 10,1
studentdetails0,0 = “Manoj” studentdetails0,1 = “Malik”
To display “Malik” we need to use the index position of the array and say , Studentdetails0,1.
Example 2.
We will create a VB.Net application, which will accept Student Name, Address and city name and display it in the text box in a formatted way.
As in the earlier example we will create a text box , change its name and its multi line property to true.
Change the text box to txtsummary. Add a button and write the below code in that.
Dim arrsummary3, 3 As String Dim i, j As Integer
As we wanted just 3 columns we have set it to 2, else if u want to be two only then while declaring the array make it 2,2 as the lower
index is 0. For i = 0 To 2
For j = 0 To 2
arrsummaryi, j = InputBoxEnter the value for i row _ and j column , Summary
Next Next
Display the values in the summary array. For i = 0 To 2
For j = 0 To 2 If txtsummary.Text = Then
txtsummary.Text = arrsummaryi, j Else
txtsummary.Text = txtsummary.Text - arrsummaryi, j End If
Next txtsummary.Text = txtsummary.Text vbCrLf
Next
Mohan 2b,4
th
lane Kanpur Mike 8
th
block csd NY Lim
Chou Lane Hong Kong
Dynamic Arrays. Till now what we read were about fixed arrays. Let us see how we can manipulate the
size of an array at run time. Many times we feel that the size of array in not enough or too much then required. As we
know that array will allocate memory location when its declared, so to release or add more we need to change the dimension of the array which has been pre-declared.
We can create a dynamic array by not specifying the size of the array at the time of array declaration.
Syntax: Dim student_names as string
In the above syntax you will see that number of elements are not mentioned. Now to re- declare the elements we make use of ReDim for an array to change its dimension.
e.g. Dim student_names as string
ReDim student_names10 ReDim can also change the size of multi-dimensional arrays.
You can change the number of dimensions in an array, but you cannot make a multi- dimensional array to a single dimension or lesser than the original dimension.
e.g. Dim student_details10,15 as string
Declaring the array ReDim student_details10,25 Resizing the array
This statement does not change the data type of the array element or initialize the new values for the array elements.
This statement can be used at the procedure level only not at the class level or module level.
ReDim statements reinitializes the value of arrays with the respective data type declared by the array.
If u have initialized the array to a some values it will be lost during the time of resizing and the default values will be restored in those elements.
E.g.
Declaring the array and initializing the value for the array
dim students_names as string = {“Rahul”}
This will display the value Rahul
msgboxstudents_names0 Now resizing the array.
ReDim students_names10
This will give a fixed size to 10 elements
msgboxstudents_names0 This will display a blank value, as during the resizing the values of the array are
reinitialized to default value of string which is blank. Now to avoid such problems we will make use of a keyword called Preserve while
resizing the array to new value. Using the above example , we will make changes in the declaration.
ReDim students_names10
The old declaration
ReDim Preserve students_names10 Students_names1 = “Alex”
Students_names2 = “Michael” Msgboxstudents_names0
This will display the value as ‘Rahul’ which we had initialized before resizing it. So Preserve will restore all the initialized value of elements declared in an array.
If the array is an two or more dimensional array , you can only change the size of the last dimension by using preserve keyword.
Dim student_details10,20 as string ReDim preserve student_details15,25
This will raise error because we are trying to change the first dimension also. So u can only change the last dimension in case of multi-dimensional array
.
Few Important methods in arrays.
Ubound and Lbound.
Ubound is to get the upper limit of an array. Lbound is to get the lower limit of an array by default lower limit is 0.
e.g.
Dim weeks As String = {Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday}
Dim upper As Integer Dim lower As Integer
upper = UBoundweeks lower = LBoundweeks
MsgBoxupper.ToString - lower.ToString You will get 6 – 0 as the answer.
If you count the number of elements initialized elements its seven, but all arrays starts with lower bound as 0. So from 0 – 6 is equal to 7 elements.
This works for single dimension , but for multi-dimensions, We make use of the following:
Getupperbound, getlowerbound these functions are methods of the array class. You can use it with single dimension also but best for multi-dimensional arrays.
Syntax : arrayname.getupperboundgetlowerbounddimension
Dimension refers to the which upperlower bound should be found, 0 for first, 1 for second and so on.
example.
Dim student_details10,20,15 Dim upperlimit as integer
upperlimit = student_details.getupperbound0 This will return 10 for the 1st row element
upperlimit = student_details.getupperbound1 This will return 20 for the 2nd row of element
For all getlowerbounddimension it will return 0 as the base lower bound is zero in .NET
6. Object Oriented Programming Concepts
