I got an error on calculations with textbox vb.net-CodePudding

I try to do some calculation with textbox but i get error on the results the right result is 3700 = 4000 -300 but i get 3667 instead of 3700 i use this code

Private Sub Txtpaid_TextChanged(sender As Object, e As EventArgs) Handles Txtpaid.TextChanged
        Dim totalcredit As Decimal
        totalcredit = Val(Txtforhim.Text) - Val(Txtpaid.Text)
        Txtforhim.Text = totalcredit.ToString
    End Sub

CodePudding user response：

Add a breakpoint to the function, so you can see exactly what the code is doing during that method. Alternatively, you can add a MsgBox() like this:

Private Sub Txtpaid_TextChanged(sender As Object, e As EventArgs) Handles Txtpaid.TextChanged
    MsgBox($"Forhim Text: {Txtforhim.Text}{vbCrLf}Forhim Value: {Val(Txtforhim.Text)}{vbCrLf}Paid Text: {Txtpaid.Text}{vbCrLf}Paid Value: {Val(Txtpaid.Text)}")

    Txtforhim.Text = (Val(Txtforhim.Text) - Val(Txtpaid.Text)).ToString()
End Sub

I also strongly recommend using Decimal.Parse() or Decimal.TryParse() instead of Val(), which can be kind of naiive.

CodePudding user response：

The code is converting the text in the TextBox controls and then finding the difference.

There are some very bad design flaws here. For one, you should be using a NumericUpDown control (aka NUD) as opposed to a TextBox. NUDs provide users a way to only enter numeric values. NUDs also have a Value property (documentation) which returns a Decimal.

You are also using the legacy Visual Basic holdover, Val. Val works by trying to convert a String but stops reading the String at the first character that it can't recognize as part of a number. So if you use a comma for a decimal point and use Val("1,23") then the result of this operation is 1 because the first character that it didn't recognize as part of a number was the comma. If you wanted to continue using TextBox controls, then you should use Decimal.TryParse (documentation).