CMP 131 Introduction to Computer Programming

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CMP 131Introduction to Computer Programming

• Violetta Cavalli-Sforza
• Week 11

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THIS WEEK

• Today
• Finish loops
• Quiz results going over ..
• Tomorrow (Tuesday) LAB 01
• Work on homework 5
• Wednesday Lecture
• Start on File Processing
• Thursday LAB 01
• More work on homework 5

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NEXT WEEK

• Quiz 4
• Wednesday May 30th
• No make-up session but possibly start classes 15
  minutes early and end 15 minutes late (since you
  have ½ hour breaks)

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Nested Selection and Repetition

• Selection (IF-THEN-ELSE, CASE) and repetition
  (FOR-DO, WHILE-DO, REPEAT-UNTIL) are commonly
  occurring programming structures
• They are frequently nested within each other
• Selection inside repetition
• Repetition inside selection

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Selection Inside Repetition

• We could have done Fibonaccis problem
  differently (not necessarily better) by
  incorporating the function in the loop

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Previous Program Fibonacci

• PROGRAM Fibonacci
• CONST Number 20
• VAR J , counter variable
• N1, N2, N3 counter variable
• integer
• BEGIN
• N1 0
• writeln('Fibonacci 0', N15)
• N2 1
• writeln('Fibonacci 1', N25)
• FOR J 2 TO Number 1 DO
• BEGIN
• N3 N1 N2
• writeln('Fibonacci',J3,'',N35)
• N1 N2
• N2 N3
• END
• readln
• END.

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New Program Fibonacci

• PROGRAM Fibonacci
• CONST Number 20
• VAR J , counter variable
• N1, N2, N3 counter variable
• integer
• BEGIN
• FOR J 0 TO Number-1 DO
• IF J 0 THEN BEGIN
• N1 0
• writeln('Fibonacci 0 0')
• END ELSE IF J 1 THEN BEGIN N2 1
• writeln('Fibonacci 1 1')
• END ELSE BEGIN
• N3 N1 N2
• writeln('Fibonacci',J3,'',N35)
• N1 N2
• N2 N3
• END
• readln

Repeated at each iteration of the loop!
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Selection Inside Repetition

• If unnecessary, avoid it. It makes for
  inefficient programs
• May be necessary and part of the design, e.g.
  Selecting a menu option inside a loop.

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• PROGRAM MenuSelect
• VAR Option char
• BEGIN
• REPEAT
• print menu of options
• writeln writeln('You have the following
  options')
• writeln(' 1 to perform action 1')
• writeln(' 2 to perform action 2')
• writeln(' ....')
• writeln(' 9 to perform action 9')
• writeln(' Q to QUIT')
• read user choice
• write('Your choice ') readln(Option)
• handle user choice
• CASE Option OF
• '1'..'9' writeln('Performing action',
  Option2)
• 'Q'
• ELSE
• writeln('Unknown option', Option2,'. Try
  again.')

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• PROGRAM MenuSelect
• VAR Option char
• BEGIN
• REPEAT
• print menu of options
• writeln writeln('You have the following
  options')
• writeln(' 1 to perform action 1')
• writeln(' 2 to perform action 2')
• writeln(' ....')
• writeln(' 9 to perform action 9')
• writeln(' Q to QUIT')
• read user choice
• write('Your choice ') readln(Option)
• handle user choice
• IF ((Option gt 1) AND (Option lt 9)) OR
  (Option Q) THEN
• CASE Option OF
• '1'..'9' writeln('Performing action',
  Option2)
• 'Q'
• END CASE

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Repetition Inside Selection

• Example
• Menu for printing out different types of pictures
• ExampleMenu for accessing other menus(selection
  inside repetition repetition inside selection)

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Selection Inside Repetition Repetition Inside
Selection

• Example Menu for accessing other menus
• Each menu is embedded inside a loop selection
  inside repetition
• Each selection contains a menu within a loop
  repetition inside selection

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• REPEAT top-level menu
• display options
• read user choice
• handle user choice CASE or IF-THEN-ELSE
  stmt
• CASE Option OF
• choice1 REPEAT
• display options
• read user choice
• handle user choice
• UNTIL exit from menu1
• ...
• choiceN REPEAT display options
• read user choice
• handle user choice
• UNTIL exit from menuN
• END CASE
• UNTIL exit top level menu
• END.

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Self-Check 1

• What is displayed by the following program
  fragment, assuming N is 5?
• FOR I 1 TO N DO BEGIN FOR J 1
  TO I DO write() writeln
  END

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Self-Check 2

• What is displayed by the following program
  fragment, assuming M is 3 and N is 5?
• FOR I N DOWNTO 1 DO BEGIN FOR J
  M DOWNTO 1 DO write()
  writeLn END

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Self-Check 3

• Show the output printed by the following nested
  loops
• FOR I 1 TO 2 DO BEGIN
  writeln(Outer 5, I 5) FOR J 1 TO
  3 DO writeln(Inner 7, I 3, J 3)
  FOR K 2 DOWNTO 1 DO writeln(Inner 7, I
  3, K 3) END

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Self-Check 4

• Write a program fragment that, given an input
  value N, displays N rows in the form 1 2 ... N, 2
  3 ... N 1, and so forth.

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• PROGRAM Check
• VAR I,J,N integer
• BEGIN
• write('What is N? ') read(N)
• FOR I 1 TO N DO
• BEGIN
• FOR J I TO I N - 1 DO
• write(J2)
• writeln
• END
• readln
• END.

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Self-Check 5

• Write a program that prints a nicely labeled
  multiplication table for the digits 1 through 9.

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• PROGRAM MultiplicationTable
• VAR I,J integer
• BEGIN
• FOR I 1 TO 9 DO
• BEGIN
• FOR J 1 TO 9 DO
• write(IJ3)
• writeln
• END
• readln
• END.

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Quiz Results

• Above Median 60.5 49.5 46.5 43 40 40 37.5
• Median 35
• Below Median 26.5 22 21.5 21 16.5 11.5 11
• Mean 32.13333333
• Total Points 80
• N 15