How do I validate a zipcode in a textbox and have the corresponding state/city output to their respective labels

Question

I'm trying to write a pretty straight forward program that pulls data from my SQL Server database. And outputs the correct state and city in they're respective labels from a valid zip code entered in a textbox.

Here's some code I was messing around with. It obviously doesn't work I was just trying out.

I was able to populate a combobox with all of the states associated with a zip/city, but that's it.

// Connection string.
String cnStr;
SqlConnection cn = new SqlConnection();

cnStr = "Data Source=000.00.000.00;Initial Catalog= ;User ID= ;Password= ";

// Assign Connection string to the connection object
cn.ConnectionString = cnStr;

// Open the connection to the SQL Server
cn.Open();

// This statement creates the command object and passes in the SQL statement
// then associates the command to the cn connection object
SqlCommand cmd = new SqlCommand("select distinct state, city from tblZipcodes order by state", cn);

// Open a DataReader
SqlDataReader rdrZip = cmd.ExecuteReader();

cn.Close();

The validation of a zipcode entered in a textbox and have the resulting state and city outputted to their respective labels, from SQL Server.

Answer 1

Always use parameters, never ever build a sql query without parameters, because it leaves your application wide open for sql injection .
You should use a where clause like this

var sql = "select distinct state, city from tblZipcodes where zipcode = @ZipCode";

using (SqlCommand cmd = new SqlCommand(sql))
{
    cmd.CommandType = CommandType.Text;
    cmd.Parameters.Add(new SqlParameter("@ZipCode", SqlDbType.VarChar) { Value = myZipCode.Text });

    SqlDataReader rdrZip = cmd.ExecuteReader();
}

Use SqlDbType.NVarChar in case your columntype is NVarChar in stead of VarChar