1. Chapter 10: Records (structs)
C++ Programming: From Problem Analysis to Program Design, Second Edition
Chapter 10: Records (structs)

2. Objectives In this chapter you will: Learn about records (structs)
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

3. C++ Data Types simple structured address integral enum floating
simple
structured
integral enum
floating
float double long double
array struct union class
char short int long bool
address
pointer reference
C++ Programming: From Problem Analysis to Program Design, Second Edition

4. C++ Data Types There are simple data types that hold only one value
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

5. Structured Data Type
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

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

7. thisAnimal 5000 .id 2037581 .name “giant panda” .genus “Ailuropoda”
5000
.id
.name “giant panda”
.genus “Ailuropoda”
.species “melanoluka”
.country “China”
.age
.weight
.health Good

8. anotherAnimal 6000 .id 5281003 .name “llama” .genus “Lama”
6000
.id
.name “llama”
.genus “Lama”
.species “peruana”
.country “Peru”
.age
.weight
.health “Excellent”

9. struct AnimalType struct AnimalType // declares a struct data type
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 ; 9

10. struct type Declaration
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.

11. More about struct type declarations
More about struct type declarations
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.

12. Accessing struct Members
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

13. Valid operations on a struct member depend only on its type
thisAnimal.age = 18;
thisAnimal.id = ;
cin >> thisAnimal.weight;
getline ( cin, thisAnimal.species );
thisAnimal.name = “giant panda”;
thisAnimal.genus[ 0 ] = toupper (thisAnimal.genus[ 0 ] ) ;
thisAnimal.age++;

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

15. Aggregate struct Operations
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

16. Examples of aggregate struct operations
Examples of aggregate struct operations
anotherAnimal = thisAnimal ; // assignment
WriteOut(thisAnimal); // value parameter
ChangeWeightAndAge(thisAnimal); // reference parameter
thisAnimal = GetAnimalData( ); // return value of function
NOW WE’LL WRITE FUNCTIONS USED HERE . . .

17. void WriteOut( /* in */ AnimalType thisAnimal)
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 << “ID # “ << thisAnimal.id << thisAnimal.name << endl ;
cout << thisAnimal.genus << thisAnimal.species << endl ;
cout << thisAnimal.country << endl ;
cout << thisAnimal.age << “ years “ << endl ;
cout << thisAnimal.weight << “ lbs. “ << endl ;
cout << “General health : “ ;
WriteWord ( thisAnimal.health ) ; } 17

18. Passing a struct Type by Reference
void ChangeAge ( /* inout */ AnimalType& thisAnimal )
// Adds 1 to age
// Precondition: thisAnimal.age is assigned
// Postcondition: thisAnimal.age == + 1 {
thisAnimal.age++ ; }

19. AnimalType GetAnimalData ( void )
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 ; } 19

20. Hierarchical Structures
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 . . .

21. struct MachineRec Information about each machine in a shop contains:
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).

22. struct StatisticsType { float failRate ;
struct DateType
{ int month ; // Assume
int day ; // Assume
int year ; // Assume };
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 ;
MachineRec machine ; 22

23. struct type variable machine
7000
5719 “DRILLING…”
.month .day .year
.failrate .lastServiced .downdays
.month .day .year
.idNumber .description . history purchaseDate cost
machine.history.lastServiced.year has value 1999

24. Another Struct Example
An example of a studentData struct:
struct studentData {
string firstName;
string lastName;
char courseGrade;
float testScore;
float programmingScore;
float GPA;
}; // NOTE THE SEMICOLON
C++ Programming: From Problem Analysis to Program Design, Second Edition

25. Declaring a struct
After you have defined a struct, you can declare variables in your program to be a that struct:
studentData student;
studentData newStudent;
C++ Programming: From Problem Analysis to Program Design, Second Edition

27. Assignment
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;
C++ Programming: From Problem Analysis to Program Design, Second Edition

28. Comparison (Relational Operators)
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) .
C++ Programming: From Problem Analysis to Program Design, Second Edition

29. Input/Output No aggregate input/output operations on a struct variable
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

30. struct Variables and Functions
A struct variable can be passed as a parameter by value or by reference
A function can return a value of type struct
C++ Programming: From Problem Analysis to Program Design, Second Edition

32. Arrays in structs Two key items are associated with a list:
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 listElem[arraySize]; //array containing the list
int listLength; //length of the list };
C++ Programming: From Problem Analysis to Program Design, Second Edition

35. Programming Example A company has six salespeople
A company has six salespeople
Every month they go on road trips to sell the company’s product
At the end of each month, the total sales for each salesperson, salesperson’s ID, and the month, are recorded in a file
At the end of each year, the manager of the company asks for a report
C++ Programming: From Problem Analysis to Program Design, Second Edition

36. Output Format
Annual Sales Report
ID QT QT QT QT4 Total
_______________________________________________________________
Total
Max Sale by SalesPerson: ID = 57373, Amount = $
Max Sale by Quarter: Quarter = 3, Amount = $
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)
C++ Programming: From Problem Analysis to Program Design, Second Edition

37. Programming Example
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

38. Input/Output
Input: file containing each salesperson’s ID, and a second file containing the sales data
Output: file containing annual sales report in the above format
C++ Programming: From Problem Analysis to Program Design, Second Edition

39. Problem Analysis Main components for each sales person:
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

40. Program Analysis (continued)
There are six people, so an array of 6 components is used
Because the program requires the company’s total sales for each quarter
We need an array of four components to store the data
C++ Programming: From Problem Analysis to Program Design, Second Edition

42. Program Analysis (continued)
Read the salespeople IDs into the array salesPersonList
Initialize the quarterly sales and total sales for each salesperson to 0
C++ Programming: From Problem Analysis to Program Design, Second Edition

43. Program Analysis (continued)
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

44. Program Analysis (continued)
Once the sales data file is processed
Calculate the total sale by salesman
Calculate the total sale by quarter
Print the report
C++ Programming: From Problem Analysis to Program Design, Second Edition

45. Algorithm Design Translates into the following algorithm
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

46. Main Algorithm Declare the variables
Declare the variables
Prompt user to enter name of file containing the salesperson’s ID data
Read the name of the input file
Open the input file
If input file does not exist, exit
Initialize the array salesPersonList by calling the function initialize
C++ Programming: From Problem Analysis to Program Design, Second Edition

47. Main Algorithm (continued)
Close input file containing salesperson’s ID
Prompt user to enter name of file containing sales data
Read the name of the input file
Open the input file
If input file does not exist, exit
Prompt user to enter name of output file
Read the name of the output file
C++ Programming: From Problem Analysis to Program Design, Second Edition

48. Main Algorithm (continued)
Open the output file
Output data to two decimal places
Process sales data
Call the function getData
C++ Programming: From Problem Analysis to Program Design, Second Edition

49. Main Algorithm (continued)
Calculate the total sale by quarter by calling the function saleByQuarter
Calculate the total sale by salesman by calling the function totalSaleByPerson
Print the report in the tabular form. Call the function printReport
Find and print the salesperson who produces the maximum sales for the year by calling the function maxSaleByPerson
C++ Programming: From Problem Analysis to Program Design, Second Edition

50. Main Algorithm (continued)
Find and print the quarter producing the maximum sale for the year by calling the function maxSaleByQuarter
Close files
C++ Programming: From Problem Analysis to Program Design, Second Edition

51. Organization of Large Programs
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

52. Include Files
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

53. Include File Example // Functions for the sales by quarter program
// Functions for the sales by quarter program
#include <iostream> // system runtime files
#include <fstream>
#include <iomanip>
#include <string>
using namespace std;
#include "salesPerson.h" // sales person header file
C++ Programming: From Problem Analysis to Program Design, Second Edition

54. System Includes vs. User Includes
Note how system files are included:
#include <iostream> // using angle brackets
Note how your header files are included:
using namespace std;
#include "salesPerson.h"
Put inside double quotes after the using statement
C++ Programming: From Problem Analysis to Program Design, Second Edition

55. Summary Struct: collection of a fixed number of components
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

56. Summary struct components are accessed by name
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
C++ Programming: From Problem Analysis to Program Design, Second Edition

57. Summary
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
C++ Programming: From Problem Analysis to Program Design, Second Edition