Control Breaks

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Chapter 07

• Control Breaks

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Understanding Control Break Logic

• Control Break a temporary detour in the logic
  of a program.
• Control Break Program a program in which a
  change in the value of a variable initiates
  special actions or causes special or unusual
  processing to occur.

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• When do you use a Control Break Program?
• When you want to organize output for programs
  that handle data records.
• How do Control Break Programs Work?
• They examine the same field in each record and
  when a different value from the one that preceded
  it is encountered, they perform a special action.

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• Control Break Report a report that lists items
  in groups with each group followed by a subtotal.
• Examples of Control Break Reports
• All employees listed in order by department
  number, in which a new page starts for each
  department
• All company clients listed in order by state of
  residence, with a count of clients after each
  states client list
• All books for sale in a bookstore in order by
  category, with a dollar total for the value of
  all books following each category of book
• All items sold in order by date of sale,
  switching ink color for each new month

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• Two Shared Traits of Control Break Reports
• 1. The records in each report are listed in order
  by a specific variable, i.e., department, state,
  category or date.
• 2. When the variable changes, the program takes
  special action, i.e., starts a new page, prints a
  count or total, or switches ink color.
• To generate a Control Break Report, your input
  records
• must be organized in sorted order based on the
  field
• that will cause the breaks.

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Performing Single-level Control Breaks

• Suppose you want to print a list of employees,
  advancing to a new page for each department.
  (Figure 7-3 through Figure 7-7)
• File name EMPSBYDEPT
• Sorted by Department
• FIELD DESCRIPTION POSITIONS DATA TYPE DECIMALS
• Department 1-2 Numeric 0
• Last Name 3-14 Character
• First Name 15-26 Character
• Figure 7-1, page 247

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• EMPLOYEES BY DEPARTMENT
• LAST NAME FIRST NAME
• XXXXXXXXXXXX XXXXXXXXXXXX
• XXXXXXXXXXXX XXXXXXXXXXXX
• XXXXXXXXXXXX XXXXXXXXXXXX
• Figure 7-2, page 247
• empRec (declare variables)
• num empDept
• char empLast
• char empFirst
• char head1 EMPLOYEES BY DEPARTMENT
• char head2 LAST NAME FIRST NAME
• num oldDept

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• Basic Logic of the Algorithm
• 1. Read the first employee record from the input
  file
• 2. Determine whether the employee belongs to the
  same department
• as the previous employee
• 3. True
• Print the employee and read the next record
• False (the employee does not belong to the same
  department)
• Print the headings on the top of the new page
• 4. Finally, you proceed to print the employees
  who belong to the new
• department

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• There is a Slight Problem in this Algorithm.
• What Is It?
• ( Think About How Variables are Stored in Memory)
• After you read in a new record, there is no way
  to look back at the previous record to determine
  whether that record had a different department
  number the previous records data has been
  replaced by the new records data.

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• How Do You Solve this Problem?
• Control Break Field a special variable that is
  created to remember the last value that was
  stored in a particular variable location.
• How Does a Control Break Field Work?
• Every time you read in a record and print it, you
  also can save the crucial part of the record that
  will signal the change or control the program
  break.

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• Why would it be incorrect to initialize oldDept
  to the value of empDept when you declare oldDept?
• Because you have not yet read in the first
  record, therefore, empDept does not yet have any
  usable value.

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• The First Two Tasks Required by all Control Break
  Routines
• 1. Performs any necessary processing for the new
  group
• 2. Updates the control break field

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Using Control Data within the Control Break Module

• In the Employees by Department Report program
  example, the control break routine printed
  constant headings at the top of each new page
  but sometimes you need to use Control Data within
  a Control Break module.
• EMPLOYEES FOR DEPARTMENT 99
• LAST NAME FIRST NAME
• XXXXXXXXXXXX XXXXXXXXXXXX
• XXXXXXXXXXXX XXXXXXXXXXXX
• XXXXXXXXXXXX XXXXXXXXXXXX
• Figure 7-8, page 252

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• The Heading Contains Two Parts
• 1. a constant beginning, (EMPLOYEES BY
  DEPARTMENT)
• 2. a variable ending (the department number)

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• Suppose you have a report where the department
  prints following the employee list for the
  department.
• EMPLOYEES FOR DEPARTMENT
• LAST NAME FIRST NAME
• XXXXXXXXXXXX XXXXXXXXXXXX
• XXXXXXXXXXXX XXXXXXXXXXXX
• XXXXXXXXXXXX XXXXXXXXXXXX
• END OF DEPARTMENT 99
• Figure 7-10, page 254

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• Footer a message that prints at the end of a
  page.
• Two Basic Rules
• 1. Headings usually require information about the
  Next Record
• 2. Footers usually require information about the
  Previous Record

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• Three Tasks Required in All Control Break
  Routines
• 1. Performs any necessary processing for the
  previous group
• (i.e., writes the footer)
• 2. Performs any necessary processing for the new
  group
• (i.e., writes the heading)
• 3. Updates the control break field
• (i.e., oldDept)
• The finishUp() module for the new program
  containing footers also requires an extra step.

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• Two Things to Note
• 1. The very first heading prints separately from
  all others at the
• beginning
• 2. The very last footer must print separately
  from all others at the end

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How to Perform Control Breaks with Totals

• Suppose you run a bookstore, and one of the files
  you maintain is called BOOKFILE, which has one
  record for every book title that you carry. Each
  record has fields such as bookTitle, bookAuthor,
  bookCategory, bookPublisher, and bookPrice.
• File Name BOOKFILE
• Sorted by Category
• FIELD DESCRIPTION POSITIONS DATA TYPE DECIMALS
• Title 1-30 Character
• Author 31-36 Character
• Category 47-56 Character
• Publisher 57-72 Character
• Price 73-77 Numeric 2
• Figure 7-12, page 257

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• Suppose you want to print out a list of all the
  books that your store carries with a total number
  of books at the bottom of the list.
• BOOK LIST
• XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
• XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
• XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
• Total number of book titles 999
• Figure 7-13, page 258

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• The bookListLoop() Module Performs Three Major
  Tasks
• 1. Prints a book title
• 2. Adds 1 to the grandTotal
• 3. Reads in the next book record

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• Suppose that you decide you want a count for each
  category of book rather than just one grand
  total.
• You need two new variables
• previousCategory
• categoryTotal
• Rolling up the Totals adding a total to a
  higher-level total

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• Performs Four of the Five Tasks required by all
  Control Break routines that include totals
• 1. Performs any necessary processing for the
  previous group
• (i.e., it prints the categoryTotal)
• 2. Rolls up the current level totals to the next
  higher level
• (i.e., it adds categoryTotal to grandTotal)
• 3. Resets the current levels totals to zero
• (i.e., the categoryTotal is set to zero)
• 4. Performs any necessary processing for the new
  group
• (i.e., there is none here)
• 5. Updates the control break field
• (i.e., previousCategory)

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• How Does the closedown( ) Module Change?
• 1. You must print the last categoryTotal
• 2. You add the count for the last category into
  the grandTotal
• Options
• (1) perform these two task as separate steps
• (2) perform the control break routine
  categoryChange() one last
• time

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• Important Notes
• This control break program works whether there
  are three categories of books or 300.
• It does not matter what the categories of books
  are.
• For example, the program never asks bookCategory
  fiction,
• instead the control of the program breaks when
  the category field
• changes and it is in no way dependent on what
  that change is.

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How to Perform Multiple-level Control Breaks

• Lets say your bookstore from the last example is
  so successful that you have a chain of them
  across the country. Everytime a sale is made you
  create a record with the fields bookTitle,
  bookCity, and bookState. You would like a report
  that prints a summary of books sold in each city
  and each state.

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• BOOK SALES BY CITY AND STATE
• Ames 200
• Des Moines 814
• Iowa City 291
• Total for IA 1305
• Chicago 1093
• Crystal Lake 564
• McHenry 213
• Springfield 365
• Total for IL 2235
• Springfield 100
• Worcester 389
• Total for MA
• Grand Total 3929
• Figure 7-16, page 262

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• Summary Report a report that does not include
  any information about individual records, but
  instead includes group totals.
• Multiple-level Control Break the normal flow of
  control breaks away to print totals in response
  to more than just one change in condition.

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• Just as the file you use to create a single-level
  control break must be presorted, so must the
  input file you use to create a multiple-level
  control break report.
• Control Break Fields
• prevCity
• prevState
• Accumulators
• cityCounter
• stateCounter
• grandTotal
• Control Break Modules
• cityBreak()
• stateBreak()

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• Every time there is a change in the bookCity
  field, the cityBreak() module performs these
  standard control break tasks
• 1. Performs any necessary processing for the
  previous group
• (i.e., prints totals for the previous city)
• 2. Rolls up the current level totals to the next
  higher level
• (i.e., adds the city count to the state count)
• 3. Resets the current levels totals to zero
• (i.e., sets the city count to zero)
• 4. Performs any necessary processing for the new
  group
• (i.e., in this case there is none)
• 5. It updates the control break field
• (i.e., sets prevCity to bookCity)

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• Within the stateBreak() module, you must perform
  one new type of task, as well as the control
  break tasks you are familiar with.
• The stateBreak() module does the following
• 1. It processes the lower-level break
• (i.e., cityBreak())
• 2. Performs any necessary processing for the
  previous group
• (i.e., prints totals for the previous state)
• 3. Rolls up the current level totals to the next
  higher level
• (i.e., adds the state count to the grand total)
• 4. Resets the current levels totals to zero
• (i.e., sets the state count to zero)
• 5. Performs any necessary processing for the new
  group
• (i.e., in this case there is none)

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• Why is It Necessary to Check bookState before
  checking bookCity?
• Because when a bookCity changes, the bookState
  also might be changing, but when bookState
  changes, it means the bookCity must be changing.
• You should always check for the major-level
  break first

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• Major-Level and Minor-Level Breaks
• If the records are sorted by bookCity within
  bookState, then a change in bookState causes a
  major-level break and a change in bookCity causes
  a minor-level break.
• What Occurs in the closedown() Module?
• 1. Perform cityBreak()
• 2. Perform stateBreak()
• 3. Print grandTotal variable

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• A Control Break Program Should Check Whether You
  Need To Complete Each of the Following Tasks with
  Modules
• 1. Performing the lower-level break, if any
• 2. Performing any control break processing for
  the previous group
• 3. Rolling up the current level totals to the
  next higher level
• 4. Resetting the current levels totals to zero
• 5. Performing any control break processing for
  the new group
• 6. Updating the control break field

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How to Perform Page Breaks

• Lets say you have a file called CUSTOMERFILE
  that contains 1,000 customers with two character
  fields that you have decided to call custLast and
  custFirst. You want to print a list of these
  customers, 60 detail lines to a page.
• What Is the Solution to this Problem?
• You will use a line-counter variable to keep
  track of the number of printed lines so that you
  can break to a new page after printing 60 lines.

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• What Happens If You Neglect to reset the
  lineCounter?
• Its value will increase with each successive
  record and never be equal to 60 again.

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• The startNewPage() module must perform only Two
  Tasks you have seen required by control break
  routines
• 1. It does not perform the lower-level break,
  because there is none
• 2. It does not perform any control break
  processing for the previous
• group, because there is none
• 3. It does not roll up the current level totals
  to the next higher level,
• because there are no totals
• 4. It does not reset the current levels totals
  to zero, because there are
• no totals
• 5. it does perform control break processing for
  the new group by
• writing headings at the top of the new page
• 6. it does update the control break field the
  line counter