Anyone here familiar with Visual Basic? I'm pretty desperate....

Google might be your friend, but stackoverflow is a programmer's lifeline...

https://stackoverflow.com/questions/10011987/invalidcastexception-was-unhandled

It means it's expecting a roman numeral and you're giving it blank or null. I bet if you entered a letter or symbol, you'd get the same error.

 

If intNumber = 1 Then
lblResult.Text = "I"
ElseIf intNumber = 2 Then
lblResult.Text = "I"

Why is 2 resulting in "I"?

Also wow VBasic's syntax looks horrendous.

 

Because he couldn't get that far...

Using the answer with two votes, do a check before you feed your method values.

1 ::beep:beep:boop:: I
Backspace ::beep:beep:boop:: null/empty BOOM
2 ::beep:beep:boop:: II

So the answer gave an if-else condition where if it fit the condition the programmer wanted, then it would feed that value to the method.

Try to pretend that computers are really dumb, so when you do a backspace, it thinks you're ready and it'll try to compute the new value (blank/null)

 

Not familiar with visual basic, but with Java you'd need a loop to handle multiple inputs.

EDIT: Quick google search shows this is not the problem.

Instead of backspacing, is there a way to clear the text input without keyboard input?
Something along the lines of resetting the variables or a .clear() method?

 

I don't know Visual Basic very well, but I suspect your problem is this line:

intNumber = txtNumber.Text

When you hit backspace after entering a number, the value is empty text and this line is not able to convert the empty text to integer.

 

Instead of backspacing, is there a way to clear the text input without keyboard input?
Something along the lines of resetting the variables or a clear() method?

 

First off, I don't know Visual Basic. I think Ruby or Python would be a better intro to CS.

https://encrypted.google.com/search?hl=en&q=isNullOrEmpty visual basic

Learning programming can be like swimming in an ocean. Just think of checks like those as libraries people before you added to make life simpler for playing around certain data types or objects because it's been done again and again.

Dog.doesRollOver?
Dog.doesLickBalls?

In this case...
String.isNullorEmpty

Then there's a bunch of libraries or documents to those libraries on how they work.

Gluck!

 

Can you print screen your entire code and upload it here?

Also, is this your first time programming? Because you may have picked the wrong language to start lol.

 

Not familiar with VB either but from your code, it seems you have a from with a textbox and you have put your code on the textchanged event. So it is probably what invisible fan is saying, it's trying to process an empty string and throwing an error.

Maybe try putting in a Msgbox just to test out when the code is triggered.

Private Sub txtNumber_TextChanged(sender As Object, e As EventArgs) Handles txtNumber.TextChanged

'declare variables

Dim intNumber As Integer

MsgBox(txtNumber.Text)

intNumber = txtNumber.Text

If intNumber = 1 Then
lblResult.Text = "I"
ElseIf intNumber = 2 Then
lblResult.Text = "I"

End If

If you get a blank message box after doing backspace then that gives you your answer. When you clear the textbox, the code is triggered. In that case you should put in some code to test and see if txtNumber.Text is empty or null before doing the assignment intNumber = txtNumber.Text

 

I agree with others saying it's cast exception, because your text box can't convert a blank to an integer.

OP, don't convert the textbox to integer at all. Your program description actually says you are converting textbox entries to Roman Numerals, not integers, anyhow. Try this:

'no variables needed

If textNumber.Text = "1" Then
lblResult.Text = "I"
ElseIf textNumber.Text ="2" Then
lblResult.Text = "II"
' and so one
Else
' no valid numeral found. Please enter 1-10

End If

If for whatever reason, you actually need to use an Integer, you need to check if that textBox can be converted to an integer or not. But, I say, forget that step and just look for string versions of "1", "2" to "10", else invalid input.

If you want to get check for proper input, you could check if it is a valid text version of a number, then check if it between 1 and 10. like this:

If Integer.TryParse(textNumber.Text, 0) AndAlso ( textNumber.Text > 0 And textNumber.Text < 11) Then

' success, an integer from 1-10
If textNumber.Text = "1" Then

lblResult.Text = "I"​

ElseIf textNumber.Text ="2" Then

lblResult.Text = "II"​

' and so one
​

Else
' input not a valid Integer, tell user to try again.
End If

 

i'm no coding expert. is it crashing if you backspace and put either 1 or 2? if not then your code just doesn't know how to handle anything else other than 1 or 2 and freaks out.

 

It sounds like you are producing an error, so just write some error handling code.

 

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