gistfile1.vb

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    AddRow("1",17)
    AddRow("2",18)
    AddRow("1",17)
    AddRow("2", 18)
    AddRow("3", 19)
    AddRow("4", 20)
    AddRow("5", 21)
    AddRow("6", 22)
    AddRow("7", 23)
    AddRow("8", 24)
    AddRow("9", 25)
    AddRow("10", 26)
    AddRow("11", 27)
    AddRow("12", 28)
    AddRow("13", 29)
    AddRow("14", 30)
    AddRow("15", 31)
    'Add System.Linq to use Linq functionality'
    'Get List of miles from collection by first converting the 'datagridviewcollection to an IEnumerable of DataGridViewRow so we can use 'Linq on it
    Dim miles as IEnumerable(of DataGridViewRow) = DataGridView1.Rows.Cast(of DataGridViewRow)
    Dim totalMiles as Integer = miles.Sum(Function(row) row.Cells(3).Value)
    'You can also merge this to one line'
    Dim totalMiles1Line as Integer = DataGridView1.Rows _
        .Cast(of DataGridViewRow) _
        .Sum(Function(r) r.Cells(3).Value)

    'The Linq code above is equivelant to the following: '
    Dim longWayTotalMiles as Integer
    For Each(Dim r as DataGridViewRow in DataGridView1.Rows)
        longWayTotalMiles += r.Cells(3)
    End For

    'If instead you put strings in Cell 3 you could do the following.'
    'Please note the parse will throw an exception if there is anything but 
    'numeric data'
    Dim totalMiles1Line as Integer = DataGridView1.Rows _
        .Cast(of DataGridViewRow) _
        .Sum(Function(r) Integer.Parse(r.Cells(3)))        

    'The linq code above is equivalent to the following '
    'The Linq code above is equivelant to the following: '
    Dim longWayTotalMilesFromString as Integer
    For Each(Dim r as DataGridViewRow in DataGridView1.Rows)
        longWayTotalMilesFromString += Integer.Parse(r.Cells(3))
    End For

    'Do with the total miles whatever you want to.'
    AddRow("TotalMiles", TotalMiles)

End Sub

Private Sub AddRow(day as String, mileage as Integer)
    Dim row as new DataGridViewRow()
    row.Cells(0).Value = day
    row.Cells(3).Value = mileage
    'DataGridView.Rows is a DataGridViewRowCollection 
    'http://msdn.microsoft.com/en-us/library/system.windows.forms.datagridviewrowcollection(v=vs.110).aspx
    DataGridView1.Rows.Add(row)
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    PrintForm1.Print()
End Sub