If condition in SQL Server

So, the SQL Query is been working as expected.

Then how can pass the value of isaudited into form.cs?

The solution to tried to implement this is:-

private bool isAudited = false;

if (isAudited)
                {
                    if (MessageBox.Show("Are you sure to delete bill", "Purchase", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
                    {
                        DeletePurchase();
                    }
                }
                else
                {
                    MessageBox.Show("You Can't Delete This Purchase", "Purchase", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }

Is this correct or you have any other suggestion?

Try this: (my changes are with different color)

set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
GO

ALTER Procedure [dbo].[Delete_New_invPurchase](
@as_ID bigint,
 @upduserid nvarchar(20),
 @modidate datetime,
 @as_preDeliveryStatus bit,
 @outputFlag bit OUT

)
AS
BEGIN

DECLARE @isAudited bit

-- Get @isAudited value from table and save it into a variable
SET @isAudited = SELECT @isAudited FROM YOUR_TABLE WHERE Blah ...blah...blah...  

IF(isaudited = 1)
BEGIN
 IF @as_preDeliveryStatus=1

 BEGIN
 DECLARE
 @rowCount INT,
 @i int,
@PID bigint,
 @batchno nvarchar(20),
 @STOCKLTYPE smallint,
 @STOCKGID int,
 @STOCK float,
 @QTY float,
 @FREEQTY float,
 @STOCKcompcode nvarchar(3),
 @STOCKdivcode nvarchar(3),
 @STOCKyearcode nvarchar(5)

 DECLARE
 @tempTable table
 (
 RowID int not null primary key identity(1,1),
 PID bigint,
 batchno nvarchar(20),
 LTYPE smallint,
 GID int,
 STOCK float,
 QTY float,
 FREEQTY float,
 compcode nvarchar(3),
 divcode nvarchar(3),
 yearcode nvarchar(5)
 )

 INSERT INTO @tempTable(PID, batchno, QTY, FREEQTY, LTYPE, STOCK, GID, compcode, divcode, yearcode)
 SELECT
INVPURCHASEITEMS.PID,
 INVPURCHASEITEMS.batchno,
 INVPURCHASEITEMS.qty,
 INVPURCHASEITEMS.FREEQTY,
 INVSTOCK.LTYPE,
 INVSTOCK.QTY AS STOCK,
 INVSTOCK.GID,
 INVSTOCK.Compcode,
 INVSTOCK.DivCode,
 INVSTOCK.Yearcode
 FROM INVPURCHASEITEMS
 INNER JOIN INVSTOCK ON INVPURCHASEITEMS.PID = INVSTOCK.PID
 INNER JOIN INVPURCHASE ON INVPURCHASE.ID = INVPURCHASEITEMS.PURCHASEID
 WHERE INVPURCHASEITEMS.PURCHASEID = @as_ID AND INVPURCHASEITEMS.isdeleted = 'False'
AND INVPURCHASE.LTYPE = INVSTOCK.LTYPE AND INVPURCHASE.YEARCODE = INVSTOCK.YEARCODE
 AND INVPURCHASE.GID = INVSTOCK.GID AND INVPURCHASEITEMS.batchno = INVSTOCK.batchno

 SET @rowCount = @@ROWCOUNT
 SET @i = 0

 WHILE (@i < @rowCount)
 BEGIN
 SET @i=@i+1
 SELECT
 @PID = PID,
 @batchno = batchno,
 @STOCKLTYPE = LTYPE,
 @STOCKGID = GID,
 @STOCK = STOCK,
 @QTY = QTY,
 @FREEQTY = FREEQTY,
 @STOCKcompcode = compcode,
 @STOCKdivcode = divcode,
 @STOCKyearcode = yearcode
 FROM @tempTable
 WHERE RowID=@i

 IF (@STOCK - (@QTY + @FREEQTY)) > 0
 BEGIN
 UPDATE INVSTOCK SET qty = @STOCK - (@QTY + @FREEQTY)
 WHERE PID = @PID AND Batchno = @batchno AND LTYPE = @STOCKLTYPE AND GID = @STOCKGID
 AND Compcode = @STOCKcompcode AND DivCode = @STOCKdivcode AND Yearcode = @STOCKyearcode
END
 ELSE
 BEGIN
 UPDATE INVSTOCK SET qty = 0
 WHERE PID = @PID AND Batchno = @batchno AND LTYPE = @STOCKLTYPE AND GID = @STOCKGID
 AND Compcode = @STOCKcompcode AND DivCode = @STOCKdivcode AND Yearcode = @STOCKyearcode
END

END
 END

 UPDATE INVPURCHASE SET isdeleted = 'True', upduserid = @upduserid, modidate = getdate()
 WHERE ID = @as_ID

UPDATE INVPURCHASEITEMS SET isdeleted = 'True'
 WHERE PURCHASEID = @as_ID

-- Setting output flag to TRUE
SET @outputFlag = 1

END

ELSE
BEGIN

-- Setting output flag to FALSE
SET @outputFlag = 0
END
END