Combo Box using SQL problem in C sharp

hey i'm using C Sharp with Sql Server 2005
i have created two table which are as

table 1( CardType): Cardcode, Description.
table 2(CreditCard):Cardcode,number, expirationdate,SecCode.

the both the table having relation between them of Cardcode.

but when i used Combo box in C sharp to display the value of CardType.description it work
but when i want to save the value of cardType.description to creditcard.cardcode it is not working
can anybody over here tell me how itz work

public partial class CreditCard : Form
{
public CreditCard()
{
InitializeComponent();
}

private void CreditCard_Load(object sender, EventArgs e)
{
// TODO: This line of code loads data into the 'inFlowDataSet.Card_Type' table. You can move, or remove it, as needed.
this.card_TypeTableAdapter.Fill(this.inFlowDataSet .Card_Type);

}

private void button1_Click(object sender, EventArgs e)
{
string ConnectionString = "Data source=MAHER-PC\\SQLEXPRESS1;Initial Catalog=inFlow;Integrated Security=true";
SqlConnection MyConnection = new SqlConnection(ConnectionString);

string SQLquery = "Insert into Credit_Card(Card_code,number,Expiration_Date,Sec_C ode)";
SQLquery += " values(@Card_code,@number,@Expiration_Date,@Sec_Co de)";

try
{
MyConnection.Open();
SqlCommand Cmd = new SqlCommand(SQLquery, MyConnection);
Cmd.Parameters.AddWithValue("@Card_code", card_TypeTableAdapter = CreditCard.Card_code comboBox1.Text.ToString());
Cmd.Parameters.AddWithValue("@number", Convert.ToInt64(textBox1.Text));
Cmd.Parameters.AddWithValue("@Expiration_Date", textBox2.Text);
Cmd.Parameters.AddWithValue("@Sec_Code", (textBox3.Text).ToUpper());
Cmd.ExecuteNonQuery();
MessageBox.Show("records successfully added", "Howdy", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
Close();
}
catch (SqlTruncateException sqlTruncateEx)
{
MessageBox.Show(sqlTruncateEx.Message);
}
catch (SqlTypeException sqlTypeEx)
{
MessageBox.Show(sqlTypeEx.Message);
}


catch (Exception er)
{
MessageBox.Show(er.Message);


//}

finally
{

MyConnection.Close();

}

}