Dry Run

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Dry Run

• You can test your program without using a
  computer by dry running it on paper
• You act as the computer following the
  instructions of the program, recording the valves
  of the variables at each stage
• You can do this with a table

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Dry Run

• The table with have column headed with the names
  of the variables in the program
• Each row in the table will be labelled with a
  line number form the program.
• The entries of each row in th e table will be
  values of the variables after the execution of
  the statement on that line
• You dont need a row for every line in the
  program, just those lines where some significant
  change to the state of the program occurs e.g a
  variable gets a new value

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Dry Run

• In this table you can record all relevant changes
  to the variables as the program progresses,
  thereby test the logic of the program / algorithm
• Do a dry run before you code your program on
  computer this way any logic errors will come to
  light during the dry run

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Example of a Dry run

• L1 Declare two variables , first num second num
• L2 Initialise both variables to 0
• L3 first num 0 second num 0
• L4 Ask user to enter first number
• L5 Assign user input to first num variable
• L6 Ask user to enter second number
• L7 Assign user input to second num variable
• L8 Add first num to second num
• L9 Print result
• Do a Dry run for this program assuming the user
  enters 17 for first number and 24 for the second

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A sample Dry Run table
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Relational Operators

• Give examples
• lt less than
• gt greater than
• lt Less than or equal to altb
• gt greater than or equal cgtd
• equals
• ! not equals 5!6
• Boolean expression TRUE or FALSE

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If then Else statements

• If ltTESTgt
• ltSTATEMENT 1 gt
• Else
• ltSTATEMENT 2 gt
• ltTESTgt is a boolean expression
• Is ltTEST? Has a false valve then ltSTATEMENT 2 gt
  is executed
• Is ltTEST? Has a false valve then ltSTATEMENT 1 gt
  is executed
• Note the indentation this makes it easier to
  read

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Nesting Layout

• To make your algorithm easier to read nest the
  statements
• If (mark gt 69)
• grade A
• Else If (mark gt 59)
• grade B
• Else If (mark gt 49)
• grade C
• Else If (mark gt 39)
• grade D
• Else
• grade F

If (mark gt 69) grade A Else If (mark
gt 59) grade B Else If (mark
gt 49) grade C Else
If (mark gt 39) grade
D Else grade
F In this alternative the psuedo code crawls
across
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Nesting of if-else and while loops

• Int number
• Number 3
• For loop 1 to 3
• if number 1
• print red
• else
• if number 2
• print green
• else
• if number 3
• print yellow
• endif
• Loop end

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More Complex Loop Tests

• Sometimes we may want to allow the user to
  terminate the program/loop
• We can do this by prompting the user with a
  question e.g imagine a user is entering a series
  of numbers which will be added to together, like
  student marks. We can ask the user the question
  (Do you want to add another student mark? )
• We assign the user response to a variable named
  e.g. continue
• Declare variable continue
• Initialise the variable Continue X
• Ask the user (Do you want to add another student
  mark? )
• Assign/store the user response to variable
  continue
• Continue user response
• While (continue Y)

Loop Body
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More Complex Loop Tests

• Sometimes you may want to include more than one
  condition in your loop tests
• In such cases you can use boolean connectives (
  and )
• E.g.
• while (continue y) (item number lt 10)
• Where item number number of items to be
  added

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Problem solving

• Understanding the problem
• The plan decide how to tackle problem -
  algorithms
• Test and Evaluate dry run and test plans

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Test Plans

• Do before you code!
• Do a test plan for every branch test e.g. if the
  else and loop statements
• Extreme values such as 0 or negative numbers are
  tested in addition to normal values. Testing
  the bounds is most efficient way for testing for
  run time errors

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• The following psuedo code / algorithm prints the
  larger of two numbers
• Do a test plan to find it a series of valves to
  be input in variables first and second .Run the
  program several times
• Int first
• Int second
• Int max
• Sring str
• Prompt user to enter an integer (please enter a
  number)
• Store the number into variable first
• Prompt user to enter a second integer (please
  enter a second number)
• Store the second number into variable second
• Max first
• if (second gt max)
• max second
• Print message to screen saying (larger of the two
  numbers is max)

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Test plan example