Programming Logic and Design Fifth Edition, Comprehensive

1
Programming Logic and Design Fifth Edition,
Comprehensive

• Chapter 8
• Control Breaks

2
Objectives

• Learn about control break logic
• Perform single-level control breaks
• Use control data within a heading
• Use control data within a footer
• Perform control breaks with totals
• Perform multiple-level control breaks

3
Understanding Control Break Logic

• Control break temporary detour in program logic
• Control break program
• Program in which a change in a variables value
  causes special or unusual processing to occur
• Helps organize output from processing data
  records
• When a grouping variable is changed, special
  actions such as subtotals and new subheadings may
  occur
• Control break report report with items in
  groups, including subtotals by group

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Figure 8-1 A control break report with totals
after each state
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Understanding Control Break Logic (continued)

• Other examples of control break reports
• Employees listed by department number
• Books for sale in a bookstore by category
• Items sold in order by date of sale
• Two traits of each report
• Records are listed in order by specific variable
• When variable changes, program takes special
  action
• Starts a new page
• Prints a count
• Switches ink color

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Understanding Control Break Logic (continued)

• Input records must be organized in sequential
  order based on the grouping field
• Sorting rearranging records in a particular order

7
Performing a Single-Level Control Break

• Example employees listed by department
• Line separates each department
• Basic program logic
• Read employees name and department number from
  input file
• Determine whether employee in same department as
  previous employee
• If yes, print the employees name
• If no, print separating line and print employee
  record
• Single-level control break a break in the logic
  of the program based on value of single variable

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Figure 8-2 Employees by department
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Performing a Single-Level Control Break
(continued)

• Control break field saves the information needed
  to determine when a break should occur
• Every time a record is read and printed, save the
  part of the record that controls the program
  break
• Compare new and old values to determine when it
  is time to print the break

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Figure 8-3 Main program logic for program that
prints employees by department
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Figure 8-4 The produceReport() module
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Performing a Single-Level Control Break
(continued)

• When a new department differs from the old one
• Department-separating line must be printed
• Control break field must be updated
• If new employee works in same department as
  previous
• Employees name printed
• Logic returns to the main program, next record
  read
• Two tasks required for all control breaks
• Processing starts after old group ends and before
  new group starts
• Control break field is updated

13
Using Control Data within a Heading

• Example display the department number in heading
  prior to starting each new department
• Helpful to use the control data within the
  heading
• Create a program
• Modify produceReport() module to print a heading
  for the new group
• Modify main program to print first heading before
  entering the main loop

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Figure 8-5 Employees by department with the
department designated before each group
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Figure 8-6 Modified produceReport() module
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Figure 8-7 Main program that prints heading for
the first department before entering the
produceReport() method
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Using Control Data within a Footer

• Example print the department number following
  the employee list for the department
• Footer message printed at end of page or section
• Headings require information about the next
  record
• Footers require information about the previous
  record

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Figure 8-8 Employees by Department including a
footer after each department
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Figure 8-9 Program that includes a call to a
method that prints a footer
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Figure 8-9 Program that includes a call to a
method that prints a footer (continued)
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Figure 8-9 Program that includes a call to a
method that prints a footer (continued)
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Figure 8-10 The processDeptEnd() method
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Using Control Data within a Footer (continued)

• When a control break occurs, the program must
• Print the footer for the previous group
• Print the heading for the new group
• Update the control break field
• For the very last group, the program must
• Print the footer for the last group
• Not print another heading
• First heading and last footer must be handled
  separately from the others

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Performing Control Breaks with Totals

• Example bookstore maintains files with one
  record for every book title
• Each record has fields that hold
• Book title
• Author
• Category
• Price
• Print a list of all books the store carries
• Total at the bottom of the list

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Figure 8-11 Book file description
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Figure 8-12 Sample Book List report
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Figure 8-13 Flowchart and pseudocode that
produces report in Figure 8-12
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Figure 8-14 Sample report that lists books by
category with category counts
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Figure 8-15 Flowchart and pseudocode for program
that lists books by category with category counts
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Figure 8-15 Flowchart and pseudocode for program
that lists books by category with category counts
(continued)
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Performing Control Breaks with Totals (continued)

• Comparing Figure 8-13 and 8-15
• New variables and constants declared
• Value of category for first book stored in
  prevCategory variable
• Every time record enters main program loop
• Program checks if record represents new category
• If next category matches previous, process as
  usual
• If next category does not match, roll up the
  totals
• After all records processed, print the total

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Performing Control Breaks with Totals (continued)

• Five tasks required in all control breaks that
  print totals
• Perform processing for previous group
• Roll up the current-level totals to next higher
  level
• Reset the current levels totals to 0
• Perform processing for new group
• Update the control break field
• When series of steps in a program is identical to
  another series of steps, place them in a method

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Figure 8-16 Program in Figure 8-15 revised to
call a module
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Figure 8-16 Program in Figure 8-15 revised to
call a module (continued)
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Performing Multiple-Level Control Breaks

• Summary report group totals, not detail records
• Multiple-level control break breaks occur for
  more than one change in condition

Figure 8-17 Report of book sales by city and
state
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Performing Multiple-Level Control Breaks
(continued)

• In this example, break occurs when
• Value of city variable changes
• Value of state variable changes
• Input file must be sorted by city within state
• At end of citys records, print total for city
• At end of states records, print total for state
• Use arrays to store book counts as well as
  control break fields

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Performing Multiple-Level Control Breaks
(continued)

• Three levels of totals
• City
• State
• Grand
• Two arrays
• Book totals
• totalCITY, totalSTATE, totalGRAND
• Previous input records
• prevCITY, prevSTATE

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Figure 8-18 Main program logic for the Book
Sales by City and State report program
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Performing Multiple-Level Control Breaks
(continued)

• cityBreak() routine performs standard tasks
• Performs processing for previous group
• Rolls up the current-level totals to next higher
  level
• Resets current levels totals to 0
• Performs processing for new group
• Updates the control break field
• stateBreak() does the same, starting with
  processing cityBreak()

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Figure 8-19 The cityBreak() method for the Book
Sales by City and State report program
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Figure 8-20 The stateBreak() method for the Book
Sales by City and State report program
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Performing Multiple-Level Control Breaks
(continued)

• Main program checks for change in city and state
  variables
• When city changes, citys name and total printed
• When state changes, states name and total
  printed
• All city totals within a state print before state
  total for same state
• Seems logical to check for change in city before
  state
• Must check for state change first

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Figure 8-21 Sample data for Book Sales report
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Performing Multiple-Level Control Breaks
(continued)

• If two cities with the same name follow each
  other
• Program will not detect new city name
• Always check major-level break first
• Records sorted by city within state change in
  state causes major-level break
• If records sorted by city within state, then
  change in city causes minor-level break
• Change in state implies a change in city
• Even if the cities have the same name

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Performing Multiple-Level Control Breaks
(continued)

• Within each break module, check if you need to
• Perform the lower-level break (if any)
• Perform control break processing for previous
  group
• Roll up the current-level totals to next higher
  level
• Reset the current-level totals to 0
• Perform any control break processing for new
  group
• Update the control break field

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Summary

• Control break a change in a variables value
  causes special actions to occur
• Control break field holds data from a previous
  record to compare to the current record
• Control data can be used in a heading or footer
• Control break report contains and prints totals
  for each group, as well as grand totals

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Summary (continued)

• For multiple-level control breaks, test for a
  major-level break before a minor-level break
• In a control break, check if lower-level breaks
  need to be processed
• Page breaks can be handled based on line counters