C Programming: From Problem Analysis to Program Design, Second Edition

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C Programming From Problem Analysis to
Program Design, Second Edition
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• Chapter 10 Records (structs)

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Objectives
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• In this chapter you will
• Learn about records (structs)
• Examine various operations on a struct
• Explore ways to manipulate data using a struct
• Learn about the relationship between a struct and
  functions
• Discover how arrays are used in a struct
• Learn how to create an array of struct items

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C Data Types
structured
simple
array struct union class
integral enum
char short int long bool
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C Data Types
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• There are simple data types that hold only one
  value
• There are structured data types that hold
  multiple values
• The array was the first example of a structured
  data type that can hold multiple values
• The structure is the second example

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Structured Data Type
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• A structured data type is a type in which each
  value is a collection of component items.
• the entire collection has a single name
• each component can be accessed individually

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C Structured Type
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• often we have related information of various
  types that wed like to store together for
  convenient access under the same identifier, for
  example . . .

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thisAnimal
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5000

.id 2037581 .name
giant panda .genus
Ailuropoda .species melanoluka .count
ry China .age
18 .weight 234.6 .health
Good
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anotherAnimal
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6000

.id 5281003 .name
llama .genus Lama .species
peruana .country Peru .age
7 .weight 278.5 .health
Excellent
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struct AnimalType
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• struct AnimalType // declares a struct data
  type
• // does not allocate memory
• long id
• string name
• string genus
• string species
  struct members
• string country
  
• int age
• float weight
• string health
• // NOTE THE SEMICOLON
• AnimalType thisAnimal // declare variables
  of AnimalType
• AnimalType anotherAnimal

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struct type Declaration
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• The struct declaration names a type and names the
  members of the struct.
• It does not allocate memory for any variables of
  that type!
• You still need to declare your struct variables.

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More about struct type declarations
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• If the struct type declaration precedes all
  functions it will be visible throughout the rest
  of the file. If it is placed within a function,
  only that function can use it.
• It is common to place struct type declarations
  with TypeNames in a (.h) header file and include
  that file (more on this later).
• It is possible for members of different struct
  types to have the same identifiers. Also a
  non-struct variable may have the same identifier
  as a structure member.

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Accessing struct Members
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• Dot ( period ) is the member selection operator.
• After the struct type declaration, the various
  members can be used in your program only when
  they are preceded by a struct variable name and a
  dot.
• EXAMPLES
• thisAnimal.weight
• anotherAnimal.country

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Valid operations on a struct member depend
only on its type
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• thisAnimal.age 18
• thisAnimal.id 2037581
• cin gtgt thisAnimal.weight
• getline ( cin, thisAnimal.species )
• thisAnimal.name giant panda
• thisAnimal.genus 0 toupper
  (thisAnimal.genus 0 )
• thisAnimal.age

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Aggregate Operation
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• is an operation on a data structure as a whole,
  as opposed to an operation on an individual
  component of the data structure

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Aggregate struct Operations
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• I/O, arithmetic, and comparisons of entire struct
  variables are NOT ALLOWED!
• Operations valid on an entire struct type
  variable
• assignment to another struct variable of same
  type,
• pass to a function as argument (by value or by
  reference),
• return as value of a function

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Examples of aggregate struct operations
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• anotherAnimal thisAnimal // assignment
• WriteOut(thisAnimal) // value parameter
• ChangeWeightAndAge(thisAnimal) // reference
  parameter
• thisAnimal GetAnimalData( ) // return value
  of function
• NOW WELL WRITE FUNCTIONS USED HERE . . .

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• void WriteOut( / in / AnimalType
  thisAnimal)
• // Prints out values of all members of thisAnimal
• // Precondition all members of thisAnimal
  are assigned
• // Postcondition all members have been
  written out
• cout ltlt ID ltlt thisAnimal.id ltlt
  thisAnimal.name ltlt endl
• cout ltlt thisAnimal.genus ltlt
  thisAnimal.species ltlt endl
• cout ltlt thisAnimal.country ltlt endl
• cout ltlt thisAnimal.age ltlt years ltlt
  endl
• cout ltlt thisAnimal.weight ltlt lbs. ltlt
  endl
• cout ltlt General health

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Passing a struct Type by Reference
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• void ChangeAge ( / inout / AnimalType
  thisAnimal )
• // Adds 1 to age
• // Precondition thisAnimal.age is assigned
  
• // Postcondition thisAnimal.age
  thisAnimal.age_at_entry 1
• thisAnimal.age

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• AnimalType GetAnimalData ( void )
• // Obtains all information about an animal from
  keyboard
• // Postcondition
• // Function value AnimalType members entered
  at kbd
• AnimalType thisAnimal
• char response
• do // have user enter all members until
  they are correct
• .
• .
• .
• while (response ! Y )
• return thisAnimal

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Hierarchical Structures
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• The type of a struct member can be another struct
  type. This is called nested or hierarchical
  structures.
• Hierarchical structures are very useful when
  there is much detailed information in each
  record.
• FOR EXAMPLE . . .

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struct MachineRec
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• Information about each machine in a shop
  contains
• an idNumber,
• a written description,
• the purchase date,
• the cost,
• and a history (including failure rate, number
  of days down, and date of last service).

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• struct DateType
• int month // Assume 1 . . 12
• int day // Assume 1 . . 31
• int year // Assume 1900 . . 2050
• struct StatisticsType
• float failRate
• DateType lastServiced // DateType is
  a struct type
• int downDays
• struct MachineRec
• int idNumber
• string description
• StatisticsType history //
  StatisticsType is a struct type
• DateType purchaseDate
• float cost

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struct type variable machine
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7000
5719 DRILLING
3 21 1995 8000.0
.02 1 25 1999 4
.month .day .year
.month .day .year
.failrate .lastServiced .downdays
.idNumber .description . history
.purchaseDate .cost
machine.history.lastServiced.year has value 1999
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Another Struct Example
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• An example of a studentData struct
• struct studentData
• string firstName
• string lastName
• char courseGrade
• float testScore
• float programmingScore
• float GPA
• // NOTE THE SEMICOLON

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Declaring a struct
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• After you have defined a struct, you can declare
  variables in your program to be a that struct
• studentData student
• studentData newStudent

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Assignment
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• You can copy one structure to another if they are
  the same type of
• student newStudent
• You can copy individual members
• newStudent.lastName student.lastName
• Or into a variable of the correct type
• thisStudentName student.lastName

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Comparison (Relational Operators)
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• Compare struct variables member-wise (NOT THE
  WHOLE STRUCTURE)
• To compare the values of student and newStudent
• if(student.firstName newStudent.firstName
• student.lastName newStudent.lastName)
• .
• .
• .

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Input/Output
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• No aggregate input/output operations on a struct
  variable
• Data in a struct variable must be read one member
  at a time
• The contents of a struct variable must be written
  one member at a time

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struct Variables and Functions
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• A struct variable can be passed as a parameter by
  value or by reference
• A function can return a value of type struct

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Arrays in structs
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• Two key items are associated with a list
• Values (elements)
• Length of the list
• Define a struct containing both items
• const arraySize 1000
• struct listType
• int listElemarraySize //array containing
  the list
• int listLength //length of the
  list

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Programming Example
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• A company has six salespeople
• Every month they go on road trips to sell the
  companys product
• At the end of each month, the total sales for
  each salesperson, salespersons ID, and the
  month, are recorded in a file
• At the end of each year, the manager of the
  company asks for a report

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Output Format
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• ----------- Annual Sales Report -------------
• ID QT1 QT2 QT3 QT4
  Total
• __________________________________________________
  _____________
• 12345 1892.00 0.00 494.00 322.00
  2708.00
• 32214 343.00 892.00 9023.00 0.00
  10258.00
• 23422 1395.00 1901.00 0.00 0.00
  3296.00
• 57373 893.00 892.00 8834.00 0.00
  10619.00
• 35864 2882.00 1221.00 0.00 1223.00
  5326.00
• 54654 893.00 0.00 392.00 3420.00
  4705.00
• Total 8298.00 4906.00 18743.00 4965.00
• Max Sale by SalesPerson ID 57373, Amount
  10619.00
• Max Sale by Quarter Quarter 3, Amount
  18743.00
• QT1 stands for quarter 1 (months 1 to 3),
  QT2 for quarter 2 (months 4 to 6), QT3 for
  quarter 3 (months 7 to 9) and QT4 for quarter 4
  (months 10 to 12)

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Programming Example
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• The salespeople IDs are stored in one file sales
  data are stored in another file
• The sales data is in the following form
• salesPersonID month saleAmount
• .
• .
• .
• Sales data are not ordered

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Input/Output
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• Input file containing each salespersons ID, and
  a second file containing the sales data
• Output file containing annual sales report in
  the above format

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Problem Analysis
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• Main components for each sales person
• ID
• Quarterly sales amount
• Total annual sales amount
• Because the components are of different types,
  group them in a struct

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Program Analysis (continued)
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• There are six people, so an array of 6 components
  is used
• Because the program requires the companys total
  sales for each quarter
• We need an array of four components to store the
  data

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Program Analysis (continued)
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• Read the salespeople IDs into the array
  salesPersonList
• Initialize the quarterly sales and total sales
  for each salesperson to 0

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Program Analysis (continued)
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• For each entry in the file containing the sales
  data
• Read ID, month, sale amount for the month
• Search salesPersonList to locate the component
  corresponding to this salesperson
• Determine the quarter corresponding to the month
• Update the sales for the quarter by adding the
  sale amount for the month

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Program Analysis (continued)
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• Once the sales data file is processed
• Calculate the total sale by salesman
• Calculate the total sale by quarter
• Print the report

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Algorithm Design
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• Translates into the following algorithm
• Initialize the array sales
• Process the sales data
• Calculate the total sale by salesman
• Calculate the total sale by quarter
• Print the report
• Calculate and print maximum sale by salesman
• Calculate and print maximum sale by quarter

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Main Algorithm
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1. Declare the variables
2. Prompt user to enter name of file containing the
   salespersons ID data
3. Read the name of the input file
4. Open the input file
5. If input file does not exist, exit
6. Initialize the array salesPersonList by calling
   the function initialize

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Main Algorithm (continued)
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1. Close input file containing salespersons ID
2. Prompt user to enter name of file containing
   sales data
3. Read the name of the input file
4. Open the input file
5. If input file does not exist, exit
6. Prompt user to enter name of output file
7. Read the name of the output file

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Main Algorithm (continued)
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• Open the output file
• Output data to two decimal places
• Process sales data
• Call the function getData

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Main Algorithm (continued)
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1. Calculate the total sale by quarter by calling
   the function saleByQuarter
2. Calculate the total sale by salesman by calling
   the function totalSaleByPerson
3. Print the report in the tabular form. Call the
   function printReport
4. Find and print the salesperson who produces the
   maximum sales for the year by calling the
   function maxSaleByPerson

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Main Algorithm (continued)
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1. Find and print the quarter producing the maximum
   sale for the year by calling the function
   maxSaleByQuarter
2. Close files

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Organization of Large Programs
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• Large programs are composed of multiple source
  files. Each source file is compiled by dev-C
  then linked into an executable program
• So that struct definitions can be used in all the
  source files, they are put in header (include
  files)
• The header file is then included in the source
  file

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Include Files
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• The include statement inserts the named file in
  this source code file
• It is typically used for definitions needed by
  the source file
• Structures are the first example of the need for
  you to use your own include file
• Using include files means that you only define
  the structure once no matter how many files it is
  used in

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Include File Example
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• // Functions for the sales by quarter program
• include ltiostreamgt // system runtime files
• include ltfstreamgt
• include ltiomanipgt
• include ltstringgt
• using namespace std
• include "salesPerson.h" // sales person header
  file

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System Includes vs. User Includes
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• Note how system files are included
• include ltiostreamgt // using angle brackets
• Note how your header files are included
• using namespace std
• include "salesPerson.h"
• Put inside double quotes after the using statement

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Summary
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• Struct collection of a fixed number of
  components
• Components can be of different types
• struct is a reserved word
• No memory is allocated for a struct memory is
  allocated for struct variables when declared
• Components of a struct are called members

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Summary
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• struct components are accessed by name
• Dot (.) operator is called the member access
  operator
• Members of a struct are accessed using the dot
  (.) operator
• The only built-in operations on a struct are the
  assignment and member access

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Summary
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• Neither arithmetic nor relational operations are
  allowed on the entire structure
• structures can be passed by value or reference
• A function can return a structure
• A structure can be a member of another structure