How to calculate all value of datagridview column in single code

  Dim sumcolumn As Integer = (From row As DataGridViewRow In DataGridView1.Rows Where row.Cells(0).FormattedValue.ToString() <> String.Empty Select Convert.ToInt32(row.Cells(0).FormattedValue)).Sum().ToString()
       

Combobox Display member and Value Member

Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        Dim key As String = DirectCast(ComboBox1.SelectedItem, KeyValuePair(Of String, String)).Key
        Dim value As String = DirectCast(ComboBox1.SelectedItem, KeyValuePair(Of String, String)).Value
        MessageBox.Show(key & "   " & value)
    End Sub

'' Add items to combobox
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim comboSource As New Dictionary(Of String, String)()
        comboSource.Add("25 Year", "Nishant")
        comboSource.Add("26 Year", "Ravi")
        comboSource.Add("27 Year", "Mohan")

        ComboBox1.DataSource = New BindingSource(comboSource, Nothing)
        ComboBox1.DisplayMember = "Value"
        ComboBox1.ValueMember = "Key"
    End Sub

Armstrong number in vb.net

        Dim x As String
        Dim y As Integer
        For index As Integer = 0 To 10000
            x = ""
            y = 0
            Dim x1 As Integer = index
            Dim s As String = x1.ToString
            Dim a(s.Length) As String
            For i As Integer = s.Length - 1 To 0 Step -1
                x = s.Substring(i, 1) & x
                y = y + (s.Substring(i, 1) * s.Substring(i, 1) * s.Substring(i, 1))
            Next
            If Val(x) = y Then
                Label1.Text = Label1.Text & vbCrLf & x
            End If
            Application.DoEvents()
        Next