Error when using WHILE Function in selecting on sQL server script

[ryanframes]

hi guys i have this code,,

declare @n int
set @n = 1
SELECT     TOP 100 PERCENT ID, purchase_id, supp_add_mat_id, mat_code, asset_no, qty, require_by, require_date, require_desc, status, pr_detail_asset, 
                      scheduled, 
		while @n <= 31
		begin 
	                CASE WHEN datepart(day, require_date) = @n THEN qty ELSE '0' END AS @n
		set @n = @n+1
		end 
FROM         dbo.t_pr_details

but the code is error coz i use the While function when selecting a data,,
plz help..