VB 2010 Conversion from string "" to type 'Double' is not valid

Question

please help me. this is a uni project and I keep getting the error "Conversion from string "" to type 'Double' is not valid." even when I made sure that everything is in the correct type, everything with a value...etc.

I want to insert some new rows in my access database, here is a picture of the table that Im trying to insert into enter image description here

and this is the code the error appears at the select statement in the sub w()

Dim c As Integer
    Dim b As Double
    Dim a, d, z As String
    a = "'" + TextBox1.Text + "'"
    b = CInt(TextBox2.Text)
    c = CInt(TextBox3.Text)
    d = "'" + TextBox4.Text + "'"
    z = "'" + ComboBox1.SelectedItem + "'"


    If ComboBox1.SelectedItem = "الجبيل" Then
        w("insert into employees (em_id,em_name,m_id,city,phone,salary,password)" & " values (" + 32111 + "," + a + "," + 12303 + "," + z + "," + c + "," + b + "," + d + ")")
    ElseIf ComboBox1.SelectedItem = "جدة" Then
        w("insert into employees (em_id,em_name,m_id,city,phone,salary,password)" & " values (" + 32111 + "," + a + "," + 12302 + "," + z + "," + c + "," + b + "," + d + ")")
    ElseIf ComboBox1.SelectedItem = "الرياض" Then
        w("insert into employees (em_id, em_name,m_id,city,phone,salary,password)" & " values (" + 32111 + "," + a + "," + 12301 + "," + z + "," + c + "," + b + "," + d + ")")
    End If
    MsgBox("تم إضافة السجل بنجاح")
    TextBox1.Clear()
    TextBox2.Clear()
    TextBox3.Clear()
    TextBox4.Clear()

the sub w("") is:

 Public Sub w(ByVal s As String)
    Dim cum As New OleDbCommand(s, con)
    cum.ExecuteNonQuery()
End Sub

problem is that it works on different forms (to diffident tables and stuff), but not in here...

what should I do?

How does two rather similar questions get asked with _**so**_ little time in-between?? — Visual Vincent, Dec 12 '16 at 18:35
Like Plutonix says you should _**really**_ use SQL parameters. However the actual reason to why you get the error is illustrated in [**this answer**](http://stackoverflow.com/a/734631/3740093). — Visual Vincent, Dec 12 '16 at 18:41
Why is the variable b declared as a double, then you try to convert text into an integer and assign that to it? And if there is no text in the textbox, doesn't it make sense that it's impossible to convert "nothing" to a number? — soohoonigan, Dec 12 '16 at 18:44

VB 2010 Conversion from string "" to type 'Double' is not valid

0 Answers0