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Chapter 3 – Control Structures: Part 1

Chapter 3 – Control Structures: Part 1.

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Chapter 3 – Control Structures: Part 1

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  1. Chapter 3 – Control Structures: Part 1 Outline3.1 Introduction3.2 Algorithms3.3 Pseudocode3.4 Control Structures3.5 if and unless Selection Structures3.6 if/else and if/elsif/else Selection Structures3.7 while and until Repetition Structures3.8 do/while and do/until Repetition Structures3.9 Formulating Algorithms: Case Study 1 (Counter-controlled repetition)3.10 Formulating Algorithms with Top-down, Stepwise Refinement: Case Study 2 (Sentinel Controlled Repetition)3.11 Formulating Algorithms with Top-down Stepwise Refinement: Case Study 3 (Nested Control Structures)3.12 Internet and World Wide Web Resources

  2. add 1 to counter $counter = $counter + 1; $total = $total + $grade; add grade to total

  3. print “Earned bonus!” print “You did not earn your bonus.” sales >= 50 sales >= 50 if selection structure true $total = $total + grade; false unless selection structure false $counter = $counter + 1; true

  4. print “You did not earn your bonus.” print “Earned bonus!” $sales >= 50 false true print “You did not earn your bonus.” print “Earned bonus!” Fig. 3.3 Flowcharting the double-selection if/else control structure.

  5. $product = 2 * $product true $product <= 1000 $product = 2 * $product $product <= 1000 false Fig. 3.4 Flowcharting the while repetition structure.

  6. 1 #!/usr/bin/perl 2 # Fig. 3.5: fig03_05.pl The do/while repetition structure repeatedly prints the value of value of variable $counter while the variable is less than or equal to 10. 3 # Using the do/while repetition structure 4 5 $counter = 1; After the each execution of the body of the loop, the control variable $counter is pre-incremented. 6 7 do { 8 print "$counter "; 9 } while ( ++$counter <= 10 ); 10 11 print "\n"; 1 2 3 4 5 6 7 8 9 10

  7. 1 #!/usr/bin/perl 2 # Fig. 3.6: fig03_06.pl 3 # Using the do/until repetition structure The do/until repetition structure repeatedly prints the value of variable $counter until the variable is equal to 0. 4 5 $counter = 10; 6 After the each execution of the body of the loop, the control variable $counter is pre-decremented. 7 do { 8 print "$counter "; 9 } until ( --$counter == 0 ); 10 11 print "\n"; 10 9 8 7 6 5 4 3 2 1

  8. print “$counter “; true ++counter <= 10 false print "$counter "; --$counter == 0 Fig. 3.7 Flowcharting the do/while repetition structure.

  9. print "$counter "; --$counter == 0 print “$counter “; false --counter == 0 true Fig. 3.7 Flowcharting the do/until repetition structure.

  10. 1 #!/usr/bin/perl 2 # Fig. 3.10: fig03_10.pl 3 # Average-sales problem with counter-controlled repetition 4 Displays a prompt to the user for the next sales amount. 5 # initialization phase The value the user inputs is stored in variable $sales. Function chomp immediately removes the newline character from the input value. 6 $total = 0; # clear total The while structure executes while $weekCounter is less than or equal to 10. 7 $weekCounter = 1; # prepare to loop 8 The program updates $total with the new $sales value entered by the user. 9 # processing phase Assigns the result of the averaging calculation to variable average. Adds 1 to variable $weekCounter so the condition in the while structure will eventually become false. 10 while ( $weekCounter <= 10 ) { # loop 10 times 11 12 # prompt for input and input a sales value 13 print "Enter sales for week $weekCounter: "; 14 chomp( $sales = <STDIN> ); 15 16 $total += $sales; # add sales to total 17 ++$weekCounter; # increment counter 18 } 19 20 $average = $total / 10; # divide to find average 21 print "\nSales averaged $average computers per week\n";

  11. Enter sales for week 1: 56 Enter sales for week 2: 52 Enter sales for week 3: 64 Enter sales for week 4: 72 Enter sales for week 5: 56 Enter sales for week 6: 58 Enter sales for week 7: 62 Enter sales for week 8: 63 Enter sales for week 9: 48 Enter sales for week 10: 52 Sales averaged 58.3 computers per week

  12. 1 #!/usr/bin/perl 2 # Fig. 3.12: fig03_12.pl 3 # Average-sales problem with sentinel-controlled repetition The until structure executes until the user enters the sentinel value. Receive input from user before entering until structure. 4 5 $total = 0; The if/else structure determines whether any values have been entered by the user. The program updates $total with the new $sales value entered by the user. 6 $weekCounter = 0; The next value is entered by the user before the end of the until structure’s body. 7 8 print "Enter sales for week or enter quit: "; If variable $weekCounter is 0, a string is output indicating that no values have been entered. 9 chomp( $sales = <STDIN> ); If values have been entered, the program calculates and outputs the average of all values. 10 11 until ( $sales eq 'quit' ) { 12 $weekCounter++; 13 $total += $sales; 14 print "Enter sales for week or enter quit: "; 15 chomp( $sales = <STDIN> ); 16 } 17 18 if ( $weekCounter != 0 ) { 19 $average = $total / $weekCounter; 20 print "\nSales averaged $average computers per week.\n"; 21 } 22 else { 23 print "\nNo sales figures were entered.\n"; 24 }

  13. Enter sales for week or enter quit: 57 Enter sales for week or enter quit: 86 Enter sales for week or enter quit: 52 Enter sales for week or enter quit: 48 Enter sales for week or enter quit: quit Sales averaged 60.75 computers per week

  14. 1 #!/usr/bin/perl 2 # Fig. 3.14: fig03_14.pl 3 # Analysis of sales results 4 The while structure executes while variable $employeeCounter is less than or equal to 10. 5 # initialize loop variables 6 $metQuota = 0; # employees who met quota 7 $didNotMeetQuota = 0; # employees who did not meet quota The conditional operator increments variable $metQuota if the user has entered yes. Variable $didNotMeetQuota is incremented if the user has entered no. 8 $employeeCounter = 1; # employee counter If variable $metQuota’s value is greater than 8, a string is output to the user indicating that holiday bonuses should be raised. 9 10 # process 10 employees; counter-controlled loop 11 while ( $employeeCounter <= 10 ) { 12 print "Enter quota result, (yes or no): "; 13 chomp( $result = <STDIN> ); 14 15 # conditional operator nested in while 16 $result eq 'yes' ? ++$metQuota : ++$didNotMeetQuota; 17 18 $employeeCounter++; 19 } 20 21 # termination phase 22 print "\nMet quota: $metQuota\n"; 23 print "Failed to meet quota: $didNotMeetQuota\n"; 24 25 if ( $metQuota > 8 ) { 26 print "Raise holiday bonuses!\n"; 27 }

  15. Enter quota result, (yes or no): yes Enter quota result, (yes or no): yes Enter quota result, (yes or no): no Enter quota result, (yes or no): yes Enter quota result, (yes or no): yes Enter quota result, (yes or no): yes Enter quota result, (yes or no): yes Enter quota result, (yes or no): yes Enter quota result, (yes or no): yes Enter quota result, (yes or no): yes Met quota: 9 Failed to meet quota: 1 Raise holiday bonuses! Enter quota result, (yes or no): no Enter quota result, (yes or no): no Enter quota result, (yes or no): no Enter quota result, (yes or no): no Enter quota result, (yes or no): yes Enter quota result, (yes or no): yes Enter quota result, (yes or no): no Enter quota result, (yes or no): no Enter quota result, (yes or no): yes Enter quota result, (yes or no): no Met quota: 3 Failed to meet quota: 7

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