این eror چیه ؟؟؟ use of unassigned local variable'

[mustafaehsani]

من از linq استفاده کردم و کد زیر دارم

 protected void Button1_Click(object sender, EventArgs e)

    {

        DataClassesDataContext db = new DataClassesDataContext();

        int cr1 = int.Parse(TextBox1.Text);

        int gr1;

        var sel1 = (from cr in db.Credits

                    join hk in db.H_Kardanis on cr.CID equals hk.CreID

                    where cr.CID == gr1

                    where hk.CreID == cr1

                    select gr1);

        int gr2;

        int cr2 = int.Parse(TextBox2.Text);

        var sel2 = (from cr in db.Credits

                    join hk in db.H_Kardanis on cr.CID equals hk.CreID

                    where cr.CID == gr2

                    where hk.CreID == cr2

                    select gr2);



        if (gr1+gr2 > 6)

            {

                DetailsView3.Visible = false;

                DetailsView4.Visible = false;



            }

        }

اما نمیدونم چرا eror زیر میده

use of unassigned local variable 'gr1'
use of unassigned local variable 'gr2'