Desk Checking

1
Desk Checking
2
Desk Checking

• Desk checking is a manual (non computerised)
  technique for checking the logic of an algorithm.
  The person performing the desk check effectively
  acts as the computer, using pen and paper to
  record results. The desk checker carefully
  follows the algorithm being careful to rigidly
  adhere to the logic specified. The desk check can
  expose problems with the algorithm.
• Desk checks are useful to check an algorithm
  (before coding) thereby confirming that the
  algorithm works as expected and saves time
  possibly writing a program that doesn't do what
  was intended. Another benefit of a desk check is
  that it confirms to the programmer/designer that
  the algorithm performs as intended.
• A desk check is normally done as a table with
  columns for
• Pseudo code line number column (Pseudo code
  doesn't normally have lines numbers, but these
  are necessary in a desk check to specify the
  line(s) being executed)
• One column per variable used. The columns should
  be in alphabetical order on variable name with
  the variable name at the top of the column. As
  the algorithm is executed, the new values of the
  variables are put in the appropriate column. Show
  working for calculations.
• A condition column. The result of the condition
  will be true (T) or false (F). As the algorithm
  is executed, conditions are evaluated and the
  details are recorded in the column. Show working
  when evaluating the conditions. This is used
  whenever a condition is evaluated - IF WHILE or
  FOR statements all have explicit or implicit
  conditions.
• An Input/Output column is used to show what is
  input by the user and displayed by the program.
  Show inputs with the variable name, a "?" and
  the value input e.g. price ? 200. Show outputs
  with the variable name, an , and the value
  displayed (or just the value displayed) e.g.
  discountPrice 180 .

3
Desk Checks vs Test Plans

• A Desk Check concentrates on the value of
  variables and the logic i.e. what is the value
  of variable x after statement n what is the next
  statement to be executed?
• A Test Plan focuses on the values of inputs and
  outputs required to test a program without
  concern for the internal workings i.e. are the
  results (outputs) correct for the inputs?.

4
Sequence Desk Check

• Example 1
• Problem Description Calculate the discounted
  price of an item purchased. (Note a problem
  description is not normally specified in a desk
  check, it is only included to assist in
  understanding the problem.)
• The following example shows desk checking
  involving sequence, executing instructions one
  after the other.
• Sequence involves executing all instructions
  once, from top to bottom, one after the other.
• Algorithm  (with line numbers added for the Desk
  Check)
• 1 calcDiscountPrice()
• 2 Input price, discountPercent
• 3 discount price discountPercent / 100
• 4 discountPrice price - discount
• 5 Display discountPrice 6 STOP

5
Sequence Desk Check

• Test Data
• Inputs price 200, discountPercent
  10.Correct results discount 20,
  discountPrice 180.

6
Selection Desk Check

• Example 2
• Problem Description Calculate the discounted
  price of an item purchased. Customers receive a
  discount of 15 on an item if the purchase price
  of the item is over 100.
• The following example shows desk checking
  involving selection using an IF.
• For an IF without an ELSE, if the condition
  evaluates to True then execution continues to the
  next line and the lines between the IF and ENDIF
  are executed (inclusive), otherwise (the
  condition is False) execution jumps from the IF
  to the ENDIF.
• Algorithm  (with line numbers added for the Desk
  Check)
• 1 calcPrice()
• 2 Input price
• 3 IF price gt 100 THEN
• 4 discount price 15 / 100
• 5 price price - discount
• 6 ENDIF
• 7 Display price 8
• STOP

7
Selection Desk Check

• Inputs price 200Correct results price
  170.

8
Selection Desk Check cont.
Inputs price 50Correct results price 50.
9
Iteration Desk Check

• Problem Description Display a table of values of
  x and x squared. X is to start at 1 and increase
  by 1 up to 3.
• The following example shows desk checking
  involving iteration (repetition) using a FOR
  loop.
• The counter variable is initialized once at the
  top of the loop, the first time through the loop.
  The implied condition is evaluated at the top of
  the loop, with execution going to the next line
  if the condition is True and going to the line
  after the ENDFOR if the condition is False. In
  this case the implied condition is x lt 3 ?. On
  the ENDFOR line the counter variable is
  incremented by 1, then program execution loops
  from the ENDFOR line, back to the FOR line.
• Algorithm (with line numbers added for the Desk
  Check)
• 1 calcSquares()
• 2 Display "X", "X Squared"
• 3 FOR x 1 TO 3 DO
• 4 xSquared x x
• 5 Display x, xSquared
• 6 ENDFOR
• 7 Display "-----------"
• 8 STOP

10
Input NoneCorrect results x 1, xSquared 1
x 2, xSquared 4 x 3, xSquared 9.
11
Example from Case Study

• 1. Dim CashPaid, Change, GrandTotal As Currency
• 2. GrandTotal txtnettotal.Text
• 3. CashPaid txtcashtendered.Text
• 4. If GrandTotal gt CashPaid Then
• 5. txtcashtendered.Text ""
• 6. Else
• 7. Change CashPaid - GrandTotal
• 8. End If

12
GrandTotal 120 CashPaid 200 Change should
80
13
Try this one

• Dim Count As Integer
• Adodc1.Recordset.MoveFirst
• Do While Not Adodc1.Recordset.EOF
• Count Count 1
• Adodc1.Recordset.MoveNext
• Loop
• txtNo_Records.Text Count
• Adodc1.Recordset.MoveFirst
• End Sub

5 records in database