How to inform user that the data to be deleted/updated has critical values?

Question

I wanted to let the user know that the data they want to delete has values.

For Example: The user wanted to delete the record "Math" subject, but there are students enrolled in that subject, so the user cannot delete the record "Math".

I wanted to know the syntax for this in c#. Yes I know how to use the "Delete" syntax, but i wanted to let the user know that the record they want to delete has some valuable infos. To let the user know that they was about to delete a critical piece of data. I know that this can also be used in VB

Private Sub btnDelete_Click(sender As Object, e As EventArgs) Handles btnDelete.Click
    If DTTable("SELECT * ", "tblSubjectsEnrolled", " WHERE CtrlNumber ='" & IDNumber & "'").Rows.Count > 0 Then
        MessageBox.Show("The subject schedule cannot be deleted, because there are still students enrolled in it!", "Delete!", MessageBoxButtons.OK, MessageBoxIcon.Error)
    Else
        If MessageBox.Show("The operation cannot be undone! Continue?", "Delete", MessageBoxButtons.YesNo, MessageBoxIcon.Question) = Windows.Forms.DialogResult.Yes Then
            RecordRow("DELETE FROM [tblOfferedSubjects] WHERE [CtrlNumber]='" & IDNumber & "'")

            btnSearch.PerformClick()
            MessageBox.Show("Record Deleted!", "Delete", MessageBoxButtons.OK, MessageBoxIcon.Asterisk)
            SelectRecord()
        End If
    End If
End Sub

Public Sub RecordRow(ByVal sql As String)
    Dim con As OleDb.OleDbConnection = New OleDb.OleDbConnection(conStr)
    Dim cmd As New OleDb.OleDbCommand
    cmd.CommandType = CommandType.Text
    cmd.CommandText = sql
    cmd.Connection = con
    con.Open()
    cmd.ExecuteNonQuery()
    con.Close()
End Sub
Public Function DTTable(ByVal sql As String, ByVal tName As String, ByVal filter As String) As DataTable
    Dim connection As New OleDb.OleDbConnection(conStr)
    Dim dataAdapter As New OleDb.OleDbDataAdapter
    Dim ds As New DataSet
    dataAdapter = New OleDb.OleDbDataAdapter(sql + " from " + tName + filter, connection)
    dataAdapter.Fill(ds, tName)
    Return ds.Tables(tName)
End Function

I wanted to use something similar in that code. I also tried converting that code to c# but i can't get the DTTable().Rows.Count > 0, because .Rows cannot be preceded by a void value. Can someone help me with this?

I showed the whole snippets of code that can help you understand the problem. PS: The shown code above isn't mine. I just used it as an example for this problem. PPS:
i wanted to restrict the user to delete the whole record. Let's say in Categories, there are sub-categories. If the user wanted to delete the category which have sub-categories, it wouldn't allow the user to delete that category, unless it doesn't have any subcategory(ies) in it.

Answer 1

As you already mentioned that you know the delete syntax, your only problem seems to be showing the message.

It is actually similar to the method used in VB.

// Delete confirmation
if (MessageBox.Show ("The operation cannot be undone! Continue?", "Delete",
        MessageBoxButtons.YesNo, MessageBoxIcon.Question)
        == DialogResult.Yes) 
{
    //Delete the row
}

For more deatils refer to:

• Displaying Message Boxes
• DataTable.Select Method (String)
• How to: Delete Rows in a DataTable