what's wrong with my C# codes in INSERT command with Parameter?

what's wrong with my C# codes in INSERT command with Parameter?

my friends , what's wrong with these codes that it appear "Input string
was not in a correct format." Error ?????????
it appears in lines witch start with * who can help me?
try
{
using (SqlConnection con = new SqlConnection(connect))
{
using (SqlCommand cmd = new SqlCommand("INSERT INTO
fact_info(fact_id, druge,price,amount,total,selldate)
VALUES (@C1, @C2, @C3, @C4, @C5 ,@C6)", con))
{
cmd.Parameters.Add(new SqlParameter("@C1",
SqlDbType.Int ));
cmd.Parameters.Add(new SqlParameter("@C2",
SqlDbType.NVarChar));
cmd.Parameters.Add(new SqlParameter("@C3",
SqlDbType.Int));
cmd.Parameters.Add(new SqlParameter("@C4",
SqlDbType.Int));
cmd.Parameters.Add(new SqlParameter("@C5",
SqlDbType.Int));
cmd.Parameters.Add(new SqlParameter("@C6",
SqlDbType.NVarChar ));
con.Open();
foreach (DataGridViewRow row in dataGridView1.Rows)
{
if (!row.IsNewRow)
{
*****cmd.Parameters["@C1"].Value =Convert
.ToInt32 ( label3.Text.Trim());
cmd.Parameters["@C2"].Value =
row.Cells[1].Value.ToString ();*****
cmd.Parameters["@C3"].Value =Convert .ToInt32
( row.Cells[2].Value.ToString ());
cmd.Parameters["@C4"].Value =Convert .ToInt32
( row.Cells[3].Value.ToString ());
cmd.Parameters["@C5"].Value =Convert .ToInt32
( row.Cells[4].Value.ToString ());
cmd.Parameters["@C6"].Value = label5.Text.Trim();
cmd.ExecuteNonQuery();
}
}
}
}
}
finally
{
MessageBox.Show("done! ");
}
}