سلام
کد شما اصلاح شد .
private void button1_Click(object sender, EventArgs e)
{
objcommand.Connection = objconnection;
objcommand.CommandText = "INSERT INTO T(NAME,FAMILY,CODE)VALUES(@_NAME,@_FAMILY,@_CODE)" ;
objconnection.Open();
objcommand.Parameters.Clear();
objcommand.Parameters.AddWithValue("@_NAME", textBox1.Text);
objcommand.Parameters.AddWithValue("@_FAMILY", textBox2.Text);
objcommand.Parameters.AddWithValue("@_CODE", textBox3.Text);
objcommand.ExecuteNonQuery();
objconnection.Close();
MessageBox.Show("مشخصات با موفقیت ثبت شد");
}