Running sql SubQueries in asp.net c# -

hello working on mycollege project , trying make user login application in asp.dot net. have 2 tables in database 1 customer full detail , other customer login detail want count row in first query , if login_id , password matches executes other query retrive , displays customer first name, on redirectedd page below have done other type of method welcomed here code

protected void login1_authenticate(object sender, authenticateeventargs e) {     sqlconnection connection = new sqlconnection(conn);     connection.open();     cmd = new sqlcommand("select count(*) customer_login login_id = @a , pass_login=@b",connection);     cmd.parameters.addwithvalue("@a", login1.username);     cmd.parameters.addwithvalue("@b", login1.password);     string user_name;     int = convert.toint32(cmd.executescalar().tostring());     if (i == 1)     {         e.authenticated = true;         cmd = new sqlcommand("select f_name customer id = (select cust_id customer_login login_id = @a)", connection);//this query runs in mssms gives error in aspx       // cmd.parameters.addwithvalue("@c",new sqlcommand ("select cust_id customer_login login_id = @a"));       //cmd.parameters.addwithvalue("@a", login1.username);          sdr = cmd.executereader();         sdr.read();         user_name = sdr["f_name"].tostring();         sdr.close();         if (session["productid"] != null)         {             session["user"] = user_name.tostring();             response.redirect("~/detail/cart.aspx");         }         else         {             response.redirect("default.aspx");         }     }     else     {         e.authenticated = false;     }  }  

the problem gives following error "incorrect syntax near keyword 'select'. must declare scalar variable "@a". " thanku

because have not assigned value @a

cmd = new sqlcommand("select f_name customer id = (select cust_id customer_login login_id = @a)", connection); cmd.parameters.addwithvalue("@a",value);