Option Explicit statement ensures whether the compiler requires all variables to be explicitly
declared or not before it use in the program.
The Option Explicit has two modes. On and Off mode. If Option Explicit mode in ON , you have to declare all the
variable before you use it in the program . If not , it will generate a
compile-time error whenever a variable that has not been declared is
encountered .If the Option Explicit mode is OFF , Vb.Net automatically create a
variable whenever it sees a variable without proper declaration.
By default the Option Explicit is On
With the Option Explicit On , you can reduce the
possible errors that result from misspelled variable names. Because in Option
Explicit On mode you have to declare each variable in the program for storing
data.
Take a look at the following programs, it will give
you a clear picture of Option Explicit.
The following program is a normal vb.net program ,
so the default mode of Option Explicit On is using. The default is Option
Explicit On , so we do not need to put it in the source code.
VB.NET Source Code
Public Class Form1
Private Sub Button1_Click(ByVal sender As
System.Object, _
ByVal e As System.EventArgs) Handles
Button1.Click
Dim someVariable As String
someVariable = "Option Explicit
ON"
MsgBox(someVariable)
End Sub
End Class
The above program , declare a String variable and
assigned a value in it and it displays.
Take a look at the following program , it is an
example of Option Explicit Of
Option Explicit Off
Public Class Form1
Private Sub Button1_Click(ByVal sender As
System.Object, _
ByVal e As System.EventArgs) Handles
Button1.Click
someVariable = "Option Explicit
ON"
MsgBox(someVariable)
End Sub
End Class
Here "someVariable" is not declared , because the Option Explicit Of , without any compiler error you can continue the program.
