Repeating what the other answers have said, your code is susceptible to SQL Injection: http://www.troyhunt.com/2013/07/everything-you-wanted-to-know-about-sql.html[^] To fix it, use a parameterized command:
cmd.CommandText = "INSERT INTO T_inTem (maSKU, tenHang, maUPC, SL, gia, maNCC, ngayIn) VALUES (@maSKU, @tenHang, @maUPC, @SL, @gia, @maNCC, @ngayIn)"
' NB: For OLEDB commands, the parameter names don't matter; only the order in which they're added.
cmd.Parameters.AddWithValue("@maSKU", maSKU)
cmd.Parameters.AddWithValue("@tenHang", tenHang)
cmd.Parameters.AddWithValue("@maUPC", maUPC)
cmd.Parameters.AddWithValue("@SL", sl)
cmd.Parameters.AddWithValue("@gia", gia)
cmd.Parameters.AddWithValue("@maNCC", maNCC)
cmd.Parameters.AddWithValue("@ngayIn", ngayIn)
cmd.ExecuteNonQuery()
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer