Pseudocode

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Pseudocode

• notes from http//www.csc.calpoly.edu/jdalbey/SW
  E/pdl_std.html

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What is Pseudocode

• structured English for describing algorithms
• simplified, half-English, half-code outline of a
  computer program
• ________________________________
• An algorithm is a sequence of steps taken to
  solve a problem.

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Definition

• pseudo
• prefix, meaning similar
• Pseudocode should not resemble any particular
  programming language
• ignore syntax and particulars of a language
• structured, formalized, condensed English
• You can design solutions without knowing a
  programming language

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Basic Constructs

• SEQUENCE one task is perfomed sequentially after
  another
• IF-THEN-ELSE decision between two alternative
  courses of action
• CASE multiway branch decision based on value of
  an expression
• WHILE loop with conditional test at beginning
• FOR loop for counting loops
• REPEAT-UNTIL loop with conditional test at bottom
  of loop

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Common Action Keywords

• Input READ, OBTAIN, GET
• Output PRINT, DISPLAY, SHOW
• Compute COMPUTE, CALCULATE, DETERMINE
• Initialize SET, INIT
• Add One INCREMENT, ADD one

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IF-THEN-ELSE Structure

• IF condition THEN
• sequence 1
• ELSE
• sequence 2
• ENDIF

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IF-THEN-ELSE Example

• IF HoursWorked gt NormalMax THEN
• DISPLAY overtime message
• ELSE
• DISPLAY regular time message
• ENDIF

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CASE Structure

• CASE expression OF
• condition 1 sequence 1
• condition 2 sequence 2
• condition n sequence n
• OTHERS default sequence
• ENDCASE

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CASE Example

• CASE Title OF
• Mr Print Mister
• Mrs Print Missus
• Miss Print Miss
• Dr Print Doctor
• OTHERS Print M.
• ENDCASE

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WHILE Structure

• WHILE condition
• sequence
• ENDWHILE

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WHILE Example

• WHILE Population lt Limit
• COMPUTE Population as Population Births -
  Deaths
• ENDWHILE

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WHILE Example

• WHILE employee.type NOT EQUAL manager AND
  personCount lt numEmployees
• INCREMENT personCount
• CALL employeeList.getPerson with personCount
  RETURNING employee
• ENDWHILE

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FOR Structure

• FOR interation bounds
• sequence
• ENDFOR

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FOR Example

• FOR each month of the year
• DISPLAY number of days
• ENDFOR
• This psuedocode is great for a high-level
  description, but doesnt help us much with the
  implementation.
• How could you write the psuedocode better?

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REPEAT-UNTIL Structure

• SET total to zero
• REPEAT
• READ Temperature
• IF Temperature gt Freezing THEN
• INCREMENT total
• ENDIF
• UNTIL Temperature lt zero
• PRINT total

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Calling Methods

• CALL keyword
• Examples
• CALL AvgAge with StudentAges
• CALL Swap with CurrentItem and TargetItem
• CALL getBalance RETURNING aBalance
• CALL Account.debit with CheckAmount

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Examples

• SET moveCount to 1
• FOR each row on the board
• FOR each column on the board
• IF gameBoard position (row, column) is occupied
  THEN
• CALL findAdjacentTiles with row, column
• INCREMENT moveCount
• ENDIF
• ENDFOR
• ENDFOR

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Examples

• GET number of bits in the binary number (HINT
  how many characters in the string?)
• SET power to start as the number of bits in the
  binary number minus 1
• SET sum to zero
• LOOP for as many number of bits in the number
• LET bit be the value at the next position
• LET term be the value of the bit 2power
• ADD term to the sum
• SET power to power minus 1
• ENDLOOP
• RETURN decimal value of sum

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Examples

• SET total to zero
• SET grade counter to zero
• OPEN file
• WHILE not at end of file
• GET grade
• ADD grade to total
• INCREMENT counter
• ENDWHILE
• CLOSE file
• SET average to total divided by counter
• PRINT average

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What do you do with it?

• Each method and class should have a flowerbox
  that states the pseudocode for that particular
  method/class.
• / Method calculates average of a list
• Inputs list of grades as integers
• Returns double-valued average
• FOR size of list
• GET current grade from list
• ADD current grade to total
• ENDFOR
• SET average to total divided by number in list
• RETURN average
• /
• public double calculateAverage( int listOfGrades
  )
• double total 0
• for( int i0 iltlistOfGrades.length i )
• total listOfGradesi
• double average total / listOfGrades.length
• return average