How to work with null value

I am trying to show data in page load. but every time i am getting error. MY CODE is -
            Dim SID As Integer = 0
            SID = Request("SID")
            Dim strSQL As String = ""
            strSQL = "SELECT LID, SurveyTypeID, CentreID, CentreScore, EnquiryDate, QCat, CommentsAfterQuestion " & _
                     "FROM dbo.QuestionDetails WHERE LID = " & SID
            Dim strCon As String = ""
            strCon = "Data Source=Test; Initial Catalog=Test; Integrated Security=True"

            Dim sqlCMD As SqlCommand = New SqlCommand(strSQL, New SqlConnection(strCon))
            Dim dr As SqlDataReader = sqlCMD.ExecuteReader()

            Do While (dr.Read())
                txtSurveyTypeID.Text = dr.GetInt32(1)
                txtCentreID.Text = dr.GetInt32(2)
                txtCentreScore.Text = dr.GetDecimal(3)              
                txtEnquiryDate.Text = dr.GetDateTime(4)
                txtQCat.Text = dr.GetInt32(5)
                txtComments.Text = dr.GetString(6)

THE Error is -

Data is Null. This method or property cannot be called on Null values.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Data.SqlTypes.SqlNullValueException: Data is Null. This method or property cannot be called on Null values.

Source Error:
Line 37:                 txtSurveyTypeID.Text = dr.GetInt32(1)
Line 38:                 txtCentreID.Text = dr.GetInt32(2)
Line 39:                 txtCentreScore.Text = dr.GetDecimal(3)
Line 40:                
Line 41:                 txtEnquiryDate.Text = dr.GetDateTime(4)

Please can anyone help me how to solve this probelm.

thanks in advance
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David H.H.LeeCommented:
Hi arifpervez,
It seem like NULL value returned from database. You can cast all the return value into string mode instead using .ToString() method.
txtCentreScore.Text = dr(3).ToString()              

arifpervezAuthor Commented:
Hi x_com
Yes its working. But If i want to update then showing error.
cmd.Parameters.Add("@CentreScore", SqlDbType.Decimal).Value = txtCentreScore.Text
error is -
System.FormatException: Failed to convert parameter value from a String to a Decimal.

what i will do with this.

David H.H.LeeCommented:
Hi arifpervez,
You can convert it to proper data type in this case.

Dim s as double


cmd.Parameters.Add("@CentreScore", SqlDbType.Decimal).Value = s

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arifpervezAuthor Commented:
I want to pass NULL instead of 0. how can i do this.
David H.H.LeeCommented:
Hi arifpervez,
First make sure your column is allow null value. Then, change the existing proposed code:

cmd.Parameters.Add("@CentreScore", SqlDbType.Decimal).Value=iif(txtCentreScore.Text.ToString="", DBNULL.value,cdbl(txtCentreScore.Text.ToString))

Check DBNULL.value property here:
arifpervezAuthor Commented:
Hi x_com
My column is allow null value. still i am getting error -

System.InvalidCastException: Conversion from string "" to type 'Double' is not valid. ---> System.FormatException: Input string was not in a correct format
arifpervezAuthor Commented:
Hi x_com

i changed CDbl to CStr. Now Its working.
Thank you for you help.
David H.H.LeeCommented:
Hi arifpervez,
Ok, i'm glad to help. Time to close this question?

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