Visual Basic 2D Array Issue - arrays

Question

I currently am having some trouble trying to get my program to work with a 2D array. I had it working earlier with a 1D array but I am totally lost now that I have to make these changes.
Below is what I currently have as my 2D array and the code that I thought would work for spitting out a letter grade but does not give me anything. Would anyone be able to tell me what I'm doing wrong?
Private strGrades(,) As String = {{"900", "A"},
{"815", "B"},
{"750", "C"},
{"700", "D"},
{"0", "F"}}
Dim strGradeSearch As String
Dim intRow As Integer
strGradeSearch = txtGrade.Text
For intRow = 0 To 4
If intRow > strGrades.GetUpperBound(0) Then
strGrades(0, intRow) = strGradeSearch
intRow += 1
End If
Next intRow
If intRow <= strGrades.GetUpperBound(0) Then
lblLetter.Text = strGrades(intRow, 0)
End If

Answer 1

Please take all the following as positive comments :-)
OK. looking at your code, there are tbh several issues. You're trying to treat strings as numbers. While a string can contain what looks like a number, it only contains a string of characters that happen to be numbers. They make sense to use, but to a computer, they aren't. There is often stuff that VB does in the background to try and make life easier, but to be honest, it can be a pain.
When comparing something like grades, you need to compare actual numbers, not strings that contain numbers. You'll potentially get unexpected results. You need to get the computer to convert the string to a number. See below.
Your loop wont actually do anything because the If statement will never execute the code inside it because intRow will never be greater than the last element of the array. Anyhow.. Onwards.
A way to convert strings to numbers is to user the Val function, though this "old" VB. The current way is to use Integer.Parse. Have a look at this link for some basic information about it.
Lets walk through what you want to do.
Get the string in the textbox.
Convert the string to a number.
Loop through the array and for each element, get the number stored as a string and convert it to a number and then compare it to the grade number.
If the grade is greater than any of the values, make a note of the
letter linked to the grade and stop searching through the loop.
Assign the letter that was found to the label.
The following code should do this
Dim strGrades(,) As String = {{"900", "A"},
{"815", "B"},
{"750", "C"},
{"700", "D"},
{"0", "F"}}
Dim intGradeSearch As Integer
Dim strGradeLetter As String = ""
intGradeSearch = Integer.Parse(TxtGrade.Text)
For i As Integer = 0 To 4
If intGradeSearch >= Integer.Parse(strGrades(i, 0)) Then
strGradeLetter = strGrades(i, 1)
Exit For
End If
Next
LblLetter.Text = strGradeLetter
End Sub
You dont need to check intRow after the loop has finished, because in this case, at some point in the loop, a grade letter will always be found if the number in the textbox is greater than or equal to a number in the array.
If you have any questions, please don't hesitate to ask.