Member Avatar for killer88

say im performing addition of two numbers.
there are three textboxes . 2 for entering the numbers and 1 for displaying the result.
im giving one value in first text box and no value in second textbox
it says "conversion not possible". now wat shuld i do to make the value as 0 in a textbox automatically if no value is entered in textbox.

  • 7 Contributors
  • 7 Replies
  • 358 Views
  • 22 Hours Discussion Span
  • Latest Post Latest Post by killer88

Dani AI

Generated

Blank or non-numeric text throws a conversion error because the parser cannot make a valid number. A clean, robust pattern is to parse safely and fall back to 0 rather than testing many string cases. That keeps your arithmetic code simple and avoids exceptions at runtime. Thanks to suggestions already posted by and for empty checks and to for calling out overflow concerns — here is a compact, safe approach you can reuse.

Use TryParse in a small helper so every TextBox becomes trivial to read as a number:

Private Function ToIntegerOrDefault(s As String, Optional def As Integer = 0) As Integer
    Dim n As Integer
    If Integer.TryParse(If(s, String.Empty).Trim(), n) Then
        Return n
    End If
    Return def
End Function

' usage
Dim a = ToIntegerOrDefault(txtNum1.Text)
Dim b = ToIntegerOrDefault(txtNum2.Text)
txtResult.Text = (a + b).ToString()

If you need decimals or specific culture handling (decimal separator), use Double.TryParse with NumberStyles and CultureInfo so parsing is explicit about which format you accept. For UI behavior, consider the options and mentioned: NumericUpDown eliminates free-text parsing, and MaskedTextBox can restrict input. If you keep plain TextBoxes, improve UX by either (a) setting the TextBox to "0" on leave when empty, or (b) showing validation feedback with an ErrorProvider in the Validating event so users know why their entry was rejected.

Quick troubleshooting checklist: always Trim() before parsing; limit input length or range to avoid overflow; prefer TryParse over exception-catching for performance; and choose control types (NumericUpDown/MaskedTextBox) when you can to remove parsing from the problem entirely. This balances safe parsing, good UX, and maintainable code.

Recommended Answers

All 7 Replies

Member Avatar for ardi_lucy

i hop do by simple checking the value of the textbox

Dim num1 As Short

    If TextBox1.Text.Equals("") Then
        num1 = 0
    End If

hop this help ;)

Edited by ardi_lucy
Member Avatar for deceptikon

Why are you using a Textbox? Just use a NumericUpDown control with the default set to 0. Not only will this correct your immediate problem, it also saves you all kinds of trouble in verifying that the "values" are actually numeric.

Edited by deceptikon
Member Avatar for xerohomicide 
    If String.IsNullOrEmpty(TextBox1.Text.Trim) Then
            value = 0
    End If
Member Avatar for tinstaafl

An simpler way, Dim num1 as Double = Val(TextBox1.Text) the Val function returns a double, but if you need it to be an Integer, you can convert it to Integer, Dim num1 as Integer = Convert.ToInt16(Val(TextBox1.Text)) It will convert any string representation of a number to a number, and if the string starts with any non digit character, or is null it will return 0

Or you could use a MaskedTextBox. It allows you to use a format string to restrict what is typed in. Something like "####0.00", will allow any digits to be entered, use the 0 to hard code the format say you want a minimum number of digits, and or decimal places. Use the # to soft code it, to restrict the mamximum number of digits, but not require a minimum. As per my example the user will have to submit at least 3 digits, 2 of them decimnal, but will allow up to 7 digits.

Edited by tinstaafl
Member Avatar for Reverend Jim 
Dim num1 As Integer
Dim num2 As Integer

If IsNumeric(txtNum1.Text) Then
    num1 = CInt(txtNum1.Text)
Else
    num1 = 0
End If    

If IsNumeric(txtNum2.Text) Then
    num2 = CInt(txtNum2.Text)
Else
    num2 = 0
End If

Or more concisely

Dim num1 As Integer = 0
If IsNumeric(txtNum1.Text) Then num1 = CInt(txtNum1.Text)
Dim num2 As Integer = 0
If IsNumeric(txtNum2.Text) Then num2 = CInt(txtNum2.Text)

You'll have to modify if the types are different, and you should limit the number of digits that can be entered to prevent overflow.

Edited by Reverend Jim
Member Avatar for azareth

or you can use masktextbox so that you can set the inputs to numbers only so you dont have to worry about variable types or mismatch and edit the max value as Jim said

and you should limit the number of digits that can be entered to prevent overflow.

just saying ..

Member Avatar for killer88

@all thanks

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.