Validate text box input for numeric range 1-100 - arrays

Question

I am trying to validate inputs to accept only a range of numbers 1-100. I have it where it will accept numbers in the range from 1-100. What I need is how to make sure character inputs such as a letter or symbol (?,/,<,> ect...) can't be used. I am using a loop to look through each input that is put into an array. When inputs are validated I am returning a blnOk = True to use in my button event to run program. I have tried double.TryParse but I can't get it to work with the array. I also have Option Strict ON. dblStudentTestScores(i) is the array that the inputs are stored in. txtTestScores(i) array is being used to tell the program which text box the loop is on so that it can gain focus with an error.
Private Sub ValidateScores()
For i = 0 To 8
If dblStudentTestScores(i) >= 0 And dblStudentTestScores(i) <= 100 Then
blnOK = True
Else
MessageBox.Show("Please Enter Test Score between 0 and 100")
txtTestScores(i).Clear()
txtTestScores(i).Focus()
txtTestScores(i).BackColor = Color.Yellow
blnOK = False
Exit Sub
End If
txtTestScores(i).BackColor = Color.White
Next
blnOK = True
End Sub
This is the code with the IsNumeric but it won't go into the Else clause. It jumps into the try catch. I would really like it to gain focus on the textbox that has the invalid input. Like it does if the number is not between 0 and 100.
Private Sub ValidateScores()
For i = 0 To 8
If CInt(IsNumeric(dblStudentTestScores(i))) >= 0 And CInt(IsNumeric(dblStudentTestScores(i))) <= 100 Then
blnOK = True
Else
MessageBox.Show("Please Enter Test Score between 0 and 100")
txtTestScores(i).Clear()
txtTestScores(i).Focus()
txtTestScores(i).BackColor = Color.Yellow
blnOK = False
Exit Sub
End If
txtTestScores(i).BackColor = Color.White
Next
blnOK = True
End Sub
Each input populates the array.
Public Sub PopulateTestScores()
'Student 1 test scores
dblStudentTestScores(0) = CDbl(txtStudent1Score1.Text)
dblStudentTestScores(1) = CDbl(txtStudent1Score2.Text)
dblStudentTestScores(2) = CDbl(txtStudent1Score3.Text)
'Student 2 test scores
dblStudentTestScores(3) = CDbl(txtStudent2Score1.Text)
dblStudentTestScores(4) = CDbl(txtStudent2Score2.Text)
dblStudentTestScores(5) = CDbl(txtStudent2Score3.Text)
'Student 3 test scores
dblStudentTestScores(6) = CDbl(txtStudent3Score1.Text)
dblStudentTestScores(7) = CDbl(txtStudent3Score2.Text)
dblStudentTestScores(8) = CDbl(txtStudent3Score3.Text)
End Sub

Answer 1

You should use double.TryParse because, if the input is not a valid double, it returns false instead of throwing an exception.
Public Function PopulateTestScores() as Boolean
Dim ok as Boolean
ok = CheckInput(txtStudent1Score1.Text, 0)
if not ok Then
txtStudent1Score1.Focus()
return ok
End if
ok = CheckInput(txtStudent1Score2.Text, 1)
if not ok Then
txtStudent1Score2.Focus()
return ok
End if
.....
return ok
End Function
private Function CheckInput(input as String, index as integer) as Boolean
Dim d as Double
Dim ok as Boolean
ok = double.TryParse(input, d)
if ok Then dblStudentTestScores(index) = d
return ok
End Function
The version of TryParse with two arguments expects the string to be in the same format of your locale (point/comma for decimals). If you want to work with different cultures then just use the appropriate TryParse overload that takes also the CultureInfo parameter.
For example, if you use the overload that takes a NumberStyles and a CultureInfo
ok = Double.TryParse(input, NumberStyles.None, CultureInfo.CurrentCulture, d)
TryParse will return false if the input doesn't match your CultureInfo and the correct convention for digit grouping.
A valid double like 10.1 in en-US culture is invalid the it-IT one where the correct input is 10,1

Answer 2

you can check the input using the isNumeric function.
https://msdn.microsoft.com/en-us/library/6cd3f6w1(v=vs.90).aspx