Select Case dlg
Case Windows.Forms.DialogResult.Yes
If TextBox12.Text = "" Then
Dim a, b, c As Integer
a = TextBox7.Text
b = TextBox8.Text //my problem
c = TextBox11.Text
TextBox12.Text = a + b - c
End If
If TextBox6.Text = "" Then
TextBox6.Text = "-"
End If
I don't know how to fix this error:
Conversion from string "" to type 'Integer' is not valid
Try using Integer.Parse:
Select Case dlg
Case Windows.Forms.DialogResult.Yes
If TextBox12.Text = "" Then
Dim a, b, c As Integer
a = Integer.Parse(TextBox7.Text)
b = Integer.Parse(TextBox8.Text) //my problem
c = Integer.Parse(TextBox11.Text)
TextBox12.Text = a + b - c
End If
If TextBox6.Text = "" Then
TextBox6.Text = "-"
End If
If Not String.IsNullOrEmpty(TextBox8.Text) Then
b = Integer.Parse(TextBox8.Text)
End If
You can check if the textbox is empty or null and then use int parse.
Or you could use Pikoh's suggestion of using Int32.TryParse
You should look at using Integer.TryParse . The advantage of using TryParse
is it won't throw an exception should the conversion fail:
Dim a As Integer = 0
Dim b As Integer = 0
Dim c As Integer = 0
Integer.TryParse(TextBox7.Text, a)
Integer.TryParse(TextBox8.Text, b)
Integer.TryParse(TextBox11.Text, c)
TextBox12.Text = (a + b - c).ToString()
You should also look at setting Option Strict On :
Restricts implicit data type conversions to only widening conversions, disallows late binding, and disallows implicit typing that results in an Object type.
This will help you write better code in the long run.
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