how to fetch statename based on country

Question

I   am working on windows form application c sharp

I am trying to fetch statename based on country in combobox

now I am stuck and my logic is not work,which place need to correction

first I fetch a country name in combobox successfully

now I am trying to fetch statename based on country but my logic is not work

 

sp : load country 

 

 

sp  : load state based on country

 

 

code: 

 private void Form1_Load_1(object sender, EventArgs e)   //load country successfully in combobox
 {
     cnnString.Open();
     SqlCommand cmd = new SqlCommand("sp_LoadCountry", cnnString);

     SqlDataReader reader = cmd.ExecuteReader();
     DataTable dt = new DataTable();
     dt.Columns.Add("countryid");
     dt.Columns.Add("countryname");
     dt.Load(reader);

     countrycomboBox.ValueMember = "countryid";
     countrycomboBox.DisplayMember = "countryname";
     countrycomboBox.DataSource = dt;

     cnnString.Close();

 }

 private void countrycomboBox_SelectedIndexChanged(object sender, EventArgs e)    //here I am stuck state not load based on country
 {
     SqlCommand cmd = new SqlCommand("sp_LoadStateBaseOnCountry", cnnString);
     cmd.CommandType = CommandType.StoredProcedure;
     cmd.Parameters.AddWithValue("countryid",countrycomboBox.Items.IndexOf(cmd));
     SqlDataAdapter da = new SqlDataAdapter(cmd);
     da.Fill(dt);
     statecomboBox.ValueMember = "stateid";
     statecomboBox.DisplayMember = "statename";
     statecomboBox.DataSource = dt;
 }

output:

 

 

now I am stuck in logic need help