How to generate invoice number in .net

//No Database Approach
int seedNum = 1;
char pad = '0';

private void Main()
{
	for(int i=0; i < 10; i ++)
	{
		Console.WriteLine("E" + seedNum.ToString().padLeft(6,pad);
		seedNum += 1;
	}
}

private string GenerateInvNo()
{
	return seedNum.ToString().PadLeft(6, pad);
}

//Database Approach

string ConnectionString = String.Format(@"Data Source = {0};User Id={1}; password={2}; Initial Catalog = {3};",
                            "DB_Server",
                            "DB_User",
                            "DB_Pass",
                            "DB_Name");
 
string query = "SELECT SeedNumber FROM YourTableName; UPDATE YourTableName SET SeedNumber = SeedNumber + 1";
 
SqlConnection connection = new SqlConnection(ConnectionString);
connection.Open();
SqlCommand queryCMD = new SqlCommand(query, connection);

int seedNum = (int)queryCMD.ExecuteScalar();
char pad = '0';

Console.WriteLine("E" + seedNum.ToString().padLeft(6,pad);

Sub generate_inv()
        Dim id_tmp As String
        Query = "select top 1 InoviceNo from Invoice order by InoviceNo desc"
        cmd = New OleDbCommand(query, cn)
        dr = cmd.ExecuteReader
        If dr.HasRows = False Then
            dr.Close()
            id_tmp = "E000001"
        Else
            dr.Read()
            id_tmp = Format(Mid(dr("InoviceNo"), 2, 6) + 1,"E00000#")
        End If
        dr.Close()
        txtInvoice.Text = id_tmp
End Sub