optional where clause

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C#

stored-procedure

I wrote this stored procedure to user filter the result of select but It wont work at all. I have a form with four textboxes and user can combinatorial fill the textboxes(user has not to fill all textboxes or one of them)so what is the problem?

CREATE PROCEDURE sp_search

  @minprice bigint=null,
  @maxprice bigint=null,
  @minarea int=null,
  @maxarea int=null,
  @location nvarchar(50)=null,
  @kind nvarchar(50)=null

AS

  SELECT * FROM Landtbl
      WHERE ((@minprice is null and @maxpriceis null) 
       or ([price] between @minprice and @maxprice))
         and
           ((@minarea is null and @maxarea is null) 
            or ([area] between @minarea and @maxarea))
              and   ((@location is null)or([location]=@location))
                and   ((@kind is null) or ([kind]=@kind))