C#

I have an array of string which is 

    string[] myarr = new[] { "a", "b", "c" };

Can you please help me how to get this result?

    a
    ab
    abc

I tried this one but I just don't know how to get the value from the array and add it on my list 

    string[] myarray = new string[] { "a", "b", "c" };
                List<string> resultarray = new List<string>();

                int i, j;
                for (i = 0; i <= myarray.Length; i++)
                {
                    for (j = i; j <= i; j++)
                    {

                        


                    }
                }

Hello, I am working on a project where I have to make connections with a smartwatch (Samsung gear s3) and a Unity application, then use the heart rate data in the Unity app. Any help is appreciated since I am experiencing problems making it work. Thank you in advance! ^^

<pre> private void btnSave_Click(object sender, EventArgs e)
        {
            SqlCeConnection connection = new SqlCeConnection();
            connection.ConnectionString = @"Data Source=C:\Users\Dell\Desktop\DataGridView\PMinfo.sdf";
            SqlCeCommand myCommand = new SqlCeCommand();
            myCommand.Connection = connection;


            for (int i = 0; i < dataGridView1.Rows.Count; i++)
            {
                myCommand.CommandText = @"INSERT into [PMinfo] (Number, CostCenter, pType, ServiceType, Receiver, WorkCenter, Start, End, Remaining, Status, ReceiveDate) values(@Number, @CostCenter, @pType, @ServiceType, @Receiver, @WorkCenter, @Start, @End, @Remaining, @Status, @ReceiveDate)";
                myCommand.Parameters.AddWithValue("@Number", dataGridView1.Rows[i].Cells[0].Value.ToString());
                myCommand.Parameters.AddWithValue("@CostCenter", dataGridView1.Rows[i].Cells[1].Value.ToString());
                myCommand.Parameters.AddWithValue("@pType", dataGridView1.Rows[i].Cells[2].Value.ToString());
                myCommand.Parameters.AddWithValue("@ServiceType", dataGridView1.Rows[i].Cells[3].Value.ToString());
                myCommand.Parameters.AddWithValue("@Receiver", dataGridView1.Rows[i].Cells[4].Value.ToString());
                myCommand.Parameters.AddWithValue("@WorkCenter", dataGridView1.Rows[i].Cells[5].Value.ToString());
                myCommand.Parameters.AddWithValue("@Start", dataGridView1.Rows[i].Cells[6].Value.ToString());
                myCommand.Parameters.AddWithValue("@End", dataGridView1.Rows[i].Cells[7].Value.ToString());
                myCommand.Parameters.AddWithValue("@Remaining", dataGridView1.Rows[i].Cells[8].Value.ToString());
                myCommand.Parameters.AddWithValue("@Status", dataGridView1.Rows[i].Cells[9].Value.ToString());
                myCommand.Parameters.AddWithValue("@ReceiveDate", dataGridView1.Rows[i].Cells[10].Value.ToString());

                connection.Open();
                myCommand.ExecuteNonQuery();
                connection.Close();
            }
        }

myCommand.ExecuteNonQuery();

'There was an error parsing the query. [ Token line number = 1,Token line offset = 92,Token in error = End ]'