using System;

using System.Data;

using System.Data.SqlClient;

public class Program

{

    public static void Main()

    {

        string city = "Chicago";

        using(SqlConnection connection = new SqlConnection())

        {

            DataSet daCustomers = new DataSet();

            SqlCommand command = new SqlCommand("SELECT * FROM Cities WHERE city = @city", connection);

            //possible options

            command.Parameters.AddWithValue("@City", city);

            //OR

            command.Parameters["@City"].Value = city;

            //OR...don't like this one that much...it's a 4 step process

            SqlParameter parameters = new SqlParameter();

            parameters.ParameterName = "@City";

            parameters.Value = city;

            command.Parameters.Add(parameters);

        }

    }

}