Insert a specific date in Mysql using vb.net - mysql

Question

Okay here is the scenario, I need to insert a specific date in mysql. Everytime I insert this date I get 0000-00-00.
Everytime a user pays between the 1st and the 20th of the month then the wb_due-date column would increment the month by 1
Ex.
I have a default value of wb_paid-date = 2013-10-15 and wb_due-date = 2013-10-20.
Now User1 Paid on 2013-10-15 and after I clicked button, the date saved on wb_due-date was 0000-00-00 instead of 2013-11-20
Take a look at my code
Function iterate(ByVal d As Date) As String
Dim m As Integer = d.Month
If d.Month >= 1 And d.Month <= 11 Then
m += 1
ElseIf d.Month = 12 Then
m = 1
End If
Return m
End Function
cmd = New MySqlCommand("INSERT INTO tbl_billing(wb_paid-date, wb_due-date)
VALUES(CURDATE(), iterate(Now.Date) , con)

Answer 1

First, let's fix your function:
Function iterate(ByVal d As DateTime) As String
Return d.AddMonths(1).ToString("yyyy-MM-dd")
End Function
Also, if you're putting a string date into command, you're almost certainly doing something wrong. Let's just do this:
Function iterate(ByVal d As DateTime) As DateTime
Return d.AddMonths(1)
End Function
Then we'll fix your Sql Command:
cmd = New MySqlCommand("INSERT INTO tbl_billing(wb_paid-date, wb_due-date) VALUES(CURDATE(), ? " , con)
cmd.Parameters.Add("?", SqlDbType.DateTime).Value = iterate(Today)