Why?
Just use the
DateTimePicker.Value property[
^] - it's already a DateTime value ready to be passed as a parameter to SQL via your INSERT query:
using (SqlConnection con = new SqlConnection(strConnect))
{
con.Open();
using (SqlCommand cmd = new SqlCommand("INSERT INTO myTable (myDateColumn, myStringColumn) VALUES (@DT, @ST)", con))
{
cmd.Parameters.AddWithValue("@DT", myDateTimePicker.Value);
cmd.Parameters.AddWithValue("@ST", myTextBox.Text);
cmd.ExecuteNonQuery();
}
}