Too many characters in character literal error in insert query

string firstname = txt_first_name.Text.Trim();
        string middlename = txt_middle_name.Text.Trim();
        string lastname = txt_last_name.Text.Trim();
        string address = txt_address.Text.Trim();
        string Mobile_No = txt_mob_no.Text.Trim();
        string birthdate = Convert.ToString(txt_birthdate.Text.Trim());
        string gender = Rdo_gender.SelectedIndex.Trim();
        string email_id = txt_email.Text.Trim();
        string user_name = txt_userid.Text.Trim();
        string password  = txt_pass.Text.Trim();
        string confirm_password = txt_confirm_pass.Text.Trim();
        string country = txt_country.Text.Trim();
        string  city = txt_city.Text.Trim();

//getting error in below query

        string querystr= "insert into DSProfile.HDR_PROFILE(first_name, middle_name,last_name , address , contact_number, birth_date, gender, email_id, user_name , password , confirm_password ,country , city)" + " values
        ('" + firstname + "','" + middlename + "', '"+lastname+"','"+ address +"','"+ Mobile_No+"','"+birthdate+"','"+gender+"','"+ email_id+"','"+user_name+"', '"+password+"','"+ confirm_password+"', '"+ country+"','"+ city+"')";