Option Strict is prevents program from automatic variable conversions, that is implicit data type conversions .

Option Strict [On Off]

By default Option Strict is Off

From the following example you can understand the use of Option Strict.

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 longNum As Long
		Dim intNum As Integer
		longNum = 12345
		intNum = longNum
		MsgBox(intNum)
	End Sub
  End Class

The above program is a normal vb.net program and is in default Option Strict Off . Because its Option Strict Off we can convert the value of Long to an Integer.

Take a look at the following program.

Option Strict On
Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles Button1.Click

        Dim longNum As Long
        Dim intNum As Integer

        longNum = 12345
        intNum = longNum

        MsgBox(intNum)
    End Sub
End Class