INTRODUCTION TO VISUAL BASIC .NET Appendix B 857

The public variables can be used across modules and also can be declared at the module-level. A public variable is declared in the following statements.

Public Dim int1 As Integer

or

Public int1 As Integer

Constants

Suppose you need to use a particular value in an application. The application needs to calculate and display the percentage of marks obtained by each student in an examination. To calculate the percentage of marks, the application needs to use the maximum score at a number of places. In this case, instead of repeating each value every time, you can use constants. A variable whose value remains the same during the execution of a program is called a constant.

To declare a constant, you can use the following statement:

Const maxMarks As Integer = 100

or

Const maxMarks = 100

Each of the previously mentioned statements declares a constant by the name maxMaks and initializes it with the value 100. These statements use a const keyword to declare a constant.

In case of any change in value, the processing of constants is faster than with variables; only the value at the point of declaring the constant needs to be changed.

You have learned about the variables and related concepts. You will now learn how to perform various operations on these variables.

Operators

A unit of code that performs an operation on one or more variables or elements is known as an operator. An operator can be used to perform various operations, such as arithmetic operations, concatenation operations, comparison operations, and logical operations.

INTRODUCTION TO VISUAL BASIC .NET Appendix B 859

declared. You can do this by using the Dim statement, the Public statement, or the Private statement. The syntax that is used to declare an array is:

Dim ArrayName (NumElements) As DataType

In the syntax mentioned, the following list contains specifications:

ArrayName. Specifies the name of the array.

NumElements. Specifies the number of elements that the array can

contain.

DataType. Specifies the data t ype of the elements. This is optional.

While declaring arrays, parentheses need to be included after the array name to differentiate an array from a variable. Consider the following code statement:

Dim intArray1(10) As Integer

An Integer array by the name intArray1, which can contain 11 elements, is declared in the code mentioned above. Why are there 11 elements and not 10 as mentioned in the code? It is because arrays are zero-based. The index number, which is between 0 and 10, adds up to 11. The code mentioned previously is part of the statement given here:

Dim IntArray () As Integer = New Integer(10) {}

Differences between Visual Basic .NET and Visual Basic 6.0 in Terms of Arrays

I will now discuss some of the basic differences between Visual Basic .NET and the earlier versions of Visual Basic in terms of arrays.By default, the starting index of an array is 0 in Visual Basic 6.0, and you can change the starting index to 1 by using the Option Base statement. In addition, the starting index for individual array declarations can be changed. The number of elements in the array is equal to the number specified during an array declaration statement plus one, if the default-starting index is set to 0. However, the starting index for every array is 0 and cannot be changed in Visual Basic .NET. The Option Base statement is not supported by Visual Basic .NET. Interoperability with arrays of other programming languages is permitted because most programming languages support zerobased arrays.

Initializing Arrays

Each element of an array is initialized as if it were a separate variable. However, if an array is not initialized, then Visual Basic .NET initializes each array element to the default value of the data type of the array.

Consider the code given here. It explains how to declare and initialize an array.

Dim booksArray1(4) As String booksArray1(0) = “Introducing VB.NET” booksArray1(1) = “Introducing ADO.NET” booksArray1(2) = “Introducing VC++.NET” booksArray1(3) = “Introducing ASP.NET” booksArray1(4) = “Introducing C#”

In the previously mentioned code, an array, booksArray1, is declared that can contain five String type elements. This arr ay stores Introducing VB.NET at index 0,

Introducing ADO.NET at index 1, Introducing VC++.NET at index 2, Introducing

ASP.NET at index 3, and Introducing C# at index 4. It may be mentioned that 0 is the starting index or the lower bound that remains fixed for all the arrays. The upper bound or the end index is 4, and it can differ from one array to another.

An array can be declared or initialized in a single line by using the new keyword provided by Visual Basic .NET. This example shows how to declare an array by using a single line of code.

Dim booksArray1() As String = {“Introducing VB.NET”, “Introducing ADO.NET”,

“Introducing VC++.NET”, “Introducing ASP.NET”, “Introducing C#”}

To retrieve the values stored in a particular index position, the index number and the name of the array needs to be specified.The following statements illustrate the point:

Dim strVar As String

strVar = booksArray1(2)

After the execution of the previously mentioned statements, the value of the String type variable, strVar, which is stored in the index position 2 in booksArray1, is retrieved.