In this exercise, you modify the Check Digit application from this chapter's Apply lesson. Use Windows to make a copy of the Check Digit Solution folder. Rename the copy Check Digit Solution$-$ForNext. Open the Check Digit Solution.sln file contained in the Check Digit Solution$-$ForNext folder. Delete the $[$EOCEXECNL$]$intGrandTotal $=$ intTotalOdd $+$ intTotalEven$[/$EOCEXECNL$]$ statement from the btnAssign$\_$Click procedure. Also delete the two Dim statements that declare the $[$EOCEXECNL$]$intTotalOdd$[/$EOCEXECNL$]$ and $[$EOCEXECNL$]$intTotalEven$[/$EOCEXECNL$]$ variables. Modify the procedure to use one For...Next loop $($rather than two For...Next loops$)$ to calculate the grand total. Save the solution and then start and test the application. $($If the user enters $978128586026,$ the btnAssign$\_$Click procedure should display $9781285860268.)$

Here is my current code that needs to be modified:

Option Explicit On

Option Strict On

Option Infer Off

Public Class frmMain

Private Sub btnAssign$\_$Click$($sender As Object, e As EventArgs$)$ Handles btnAssign.Click

$\text{'}$ Assign a check digit to an ISBN.

Dim strIsbn As String

Dim intDigit As Integer

Dim intTotalOdd As Integer

Dim intTotalEven As Integer

Dim intGrandTotal As Integer

Dim intRemainder As Integer

Dim intCheckDigit As Integer

If txtIsbn.Text.Length $=12$ Then

strIsbn $=$ txtIsbn.Text

For intOdd As Integer $=1$ To $11$ Step $2$

Integer.TryParse$($strIsbn$($intOdd$),$ intDigit$)$

intTotalOdd $+=($intDigit $*3)$

Next intOdd

For intEven As Integer $=0$ To $10$ Step $2$

Integer.TryParse$($strIsbn$($intEven$),$ intDigit$)$

intTotalEven $+=$ intDigit

intGrandTotal $=$ intTotalOdd $+$ intTotalEven

intRemainder $=$ intGrandTotal Mod $10$

Next

If intRemainder $<>0$ Then

intCheckDigit $=10-$ intRemainder

End If

lblFinalIsbn.Text $=$ strIsbn & intCheckDigit.ToString

Else

MessageBox.Show$("$Please enter $12$ numbers.", "Check Digit",

MessageBoxButtons.OK$,$ MessageBoxIcon.Information$)$

End If

End Sub

Private Sub btnExit$\_$Click$($sender As Object, e As EventArgs$)$ Handles btnExit.Click

Me$.$Close$()$

End Sub

Private Sub txtIsbn$\_$Enter$($sender As Object, e As EventArgs$)$ Handles txtIsbn.Enter

txtIsbn.SelectAll$()$

End Sub

Private Sub txtIsbn$\_$TextChanged$($sender As Object, e As EventArgs$)$ Handles txtIsbn.TextChanged

lblFinalIsbn.Text $=$ String.Empty

End Sub

Private Sub txtIsbn$\_$KeyPress$($sender As Object, e As KeyPressEventArgs$)$ Handles txtIsbn.KeyPress

$\text{'}$ Allow only numbers and the Backspace key.

If $($e$.$KeyChar $<"0"$ OrElse e$.$KeyChar $>"9")$ AndAlso e$.$KeyChar $<>$ ControlChars.Back Then

e$.$Handled $=$ True

End If

End Sub

End Class