how to get data in one ComboBox on selection of another combobox in c# windows forms

I have 2 combobox. I want to get data in second combobox on selection of first combobox but i am not getting the data in second combobox.

I am writing the code as following:

First Combobox=cmbCat

Second Combobox=cmbSCat1

 private void GetCategory()

        {

            SqlDataAdapter da = new SqlDataAdapter("select * from Category ", con);

            DataTable dt = new DataTable();

            da.Fill(dt);

            cmbCat.DataSource = dt;

            cmbCat.DisplayMember = "Category";

            cmbCat.ValueMember = "CId";

        }

   private void cmbCat_SelectedIndexChanged(object sender, EventArgs e)

        {         

            string ik = cmbCat.SelectedText.ToString();

            if (ik != "")

            {

  SqlDataAdapter da = new SqlDataAdapter("select SId,SUbCatName from SubCategory sc inner join Category c on sc.CId =c.CId where sc.CId=c.CId and c.Category='" + cmbCat.SelectedText.ToString() + "'", con);

                DataTable dt = new DataTable();

                da.Fill(dt);

                cmbSCat1.DataSource = dt;

                cmbSCat1.DisplayMember = "SubCatName";

                cmbSCat1.ValueMember = "SId";

            }

        }

what is the error please suggest me.