Concepts related to structures in c++

1. Records (structs)
CS103- Computer Programming

2. 2
Structures
• A Structure is a collection of related data items, possibly of
different types.
• A structure type in C++ is called struct.
• A struct is heterogeneous in that it can be composed of
data of different types.
• In contrast, array is homogeneous since it can contain only
data of the same type.

3. 3
Structures
• Structures hold data that belong together.
• Examples:
– Student record: student id, name, major, gender, start year, …
– Bank account: account number, name, currency, balance, …
– Address book: name, address, telephone number, …
• In database applications, structures are called records.

4. 4
Structures
• Individual components of a struct type are called members
(or fields).
• Members can be of different types (simple, array or struct).
• A struct is named as a whole while individual members are
named using field identifiers.
• Complex data structures can be formed by defining arrays
of structs.

5. 5
struct basics
• Definition of a structure:
struct <struct-type>{
<type> <identifier_list>;
<type> <identifier_list>;
...
} ;
• Example:
struct Date {
int day;
int month;
int year;
} ;
The “Date” structure
has 3 members,
day, month & year.
Each identifier
defines a member
of the structure.

6. 6
struct examples
• Example:
struct StudentInfo{
int Id;
int age;
char Gender;
double CGA;
};
• Example:
struct StudentGrade{
char Name[15];
char Course[9];
int Lab[5];
int Homework[3];
int Exam[2];
};
The “StudentGrade”
structure has 5
members of
different array types.
The “StudentInfo”
structure has 4 members
of different types.

7. 7
struct examples
• Example:
struct BankAccount{
char Name[15];
int AcountNo[10];
double balance;
Date Birthday;
};
• Example:
struct StudentRecord{
char Name[15];
int Id;
char Dept[5];
char Gender;
};
The “StudentRecord”
structure has 4
members.
The “BankAcount”
structure has simple,
array and structure
types as members.

8. 8
struct basics
• Declaration of a variable of struct type:
<struct-type> <identifier_list>;
• Example:
StudentRecord Student1, Student2;
Student1 and Student2 are variables of
StudentRecord type.
Student1 Student2
Name
Id Gender
Dept
Name
Id Gender
Dept

9. 9
Chan Tai Man
12345 M
COMP
Ex. 1: struct basics
• The members of a struct type variable
are accessed with the dot (.) operator:
<struct-variable>.<member_name>;
• Example:
strcpy(Student1.Name, "Chan Tai Man");
Student1.Id = 12345;
strcpy(Student1.Dept, "COMP");
Student1.gender = 'M';
cout << "The student is ";
switch (Student1.gender){
case 'F': cout << "Ms. "; break;
case 'M': cout << "Mr. "; break;
}
cout << Student1.Name << endl;
Student1
Name
Id Gender
Dept

10. Records (structs)
• struct: collection of a fixed number of components
(members), accessed by name
– Members may be of different types
• Syntax:
10

11. Records (structs) (cont'd.)
• A struct is a definition, not a declaration
11

12. Records (structs) (cont'd.)
12

13. Accessing struct Members
• The syntax for accessing a struct member is:
• The dot (.) is an operator, called the member access
operator
13

14. Accessing struct Members (cont'd.)
• To initialize the members of newStudent:
newStudent.GPA = 0.0;
newStudent.firstName = "John";
newStudent.lastName = "Brown";
14

15. Accessing struct Members (cont'd.)
• More examples:
cin >> newStudent.firstName;
cin >> newStudent.testScore >>
newStudent.programmingScore;
score = (newStudent.testScore +
newStudent.programmingScore) / 2;
15

16. Accessing struct Members (cont'd.)
if (score >= 90)
newStudent.courseGrade = 'A';
else if (score >= 80)
newStudent.courseGrade = 'B';
else if (score >= 70)
newStudent.courseGrade = 'C';
else if (score >= 60)
newStudent.courseGrade = 'D';
else
newStudent.courseGrade = 'F';
16

17. Example Movie Struct
// example about structures
#include <iostream>
#include <string>
using namespace std;
struct movies_t {
string title;
int year;
} mine, yours;
void printmovie (movies_t movie);
int main ()
{
string mystr;
mine.title = "2001 A Space
Odyssey";
mine.year = 1968;
cout << "Enter title: ";
getline (cin,yours.title);
cout << "Enter year: ";
getline (cin,mystr);
cin>> yours.year;
cout << "My favorite movie is:n ";
printmovie (mine);
cout << "And yours is:n ";
printmovie (yours);
return 0;
}
void printmovie (movies_t movie)
{
cout << movie.title;
cout << " (" << movie.year <<
")n";
}
17

18. Example Conti…
Enter title: Alien
Enter year: 1979
My favorite movie is:
2001 A Space Odyssey (1968)
And yours is:
Alien (1979)
18

19. Assignment
• Value of one struct variable can be assigned to another
struct variable of the same type using an assignment
statement
• The statement:
student = newStudent;
copies the contents of newStudent into student
19

20. Assignment (cont'd.)
• The assignment statement:
student = newStudent;
is equivalent to the following
statements:
student.firstName = newStudent.firstName;
student.lastName = newStudent.lastName;
student.courseGrade = newStudent.courseGrade;
student.testScore = newStudent.testScore;
student.programmingScore =
newStudent.programmingScore;
student.GPA = newStudent.GPA;
20

21. Comparison (Relational Operators)
• Compare struct variables member-
wise
– No aggregate relational operations allowed
• To compare the values of student and
newStudent:
21

22. Input/Output
• 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
22

23. 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
23

24. Arrays versus structs
24

25. Arrays in structs
• Two key items are associated with a list:
– Values (elements)
– Length of the list
• Define a struct containing both items:
25

26. Arrays in structs (cont'd.)
26

27. 27
Arrays in structs (cont'd.)

28. structs in Arrays
28

29. 29
structs in Arrays (cont’d.)

30. 30
structs in Arrays (cont’d.)

31. structs within a struct
31
versus

32. Structs, and Pointer Variables
• You can declare pointers to other data types:
– student is an object of type studentType;
studentPtr is a pointer variable of type studentType
32

33. Structs, and Pointer Variables (cont'd.)
• To store address of student in studentPtr:
studentPtr = &student;
• To store 3.9 in component gpa of student:
(*studentPtr).gpa = 3.9;
– () used because dot operator has higher precedence than
dereferencing operator
– Alternative: use member access operator arrow (->)
33

34. Movie Example
// pointers to structures
#include <iostream>
#include <string>
using namespace std;
struct movies_t {
string title;
int year;
};
int main ()
{
string mystr;
movies_t amovie;
movies_t * pmovie;
pmovie = &amovie;
cout << "Enter title: ";
getline (cin, pmovie->title);
cout << "Enter year: ";
getline (cin, mystr);
(stringstream) mystr >>
pmovie->year;
cout << "nYou have
entered:n";
cout << pmovie->title;
cout << " (" << pmovie-
>year << ")n";
return 0;
}
34

35. Example Output…
Enter title: Invasion of the body snatchers
Enter year: 1978
You have entered:
Invasion of the body snatchers (1978)
35

36. Example …
pmovie->title is equivalent to (*pmovie).title
*pmovie.title is equivalent to *(pmovie.title)
36

37. Pointers & Structs
Expression What is evaluated Equivalent
a.b Member b of object a
a->b Member b of object pointed by a (*a).b
*a.b Value pointed by member b of object a *(a.b)
37

38. Structs & File Handling
• A file may be read record by record.
38

39. COMPLETE EXAMPLE OF POINT
39

40. Point Struct
with functions
struct Point{
int x;
int y;
void init(){
x=0;
y=0;
}
void init(int a, int b) // Overloaded
Function
{
x=a;
y=b;
}
void input(){
cout<<"nEnter value of X: ";
cin>>x;
cout<<"nEnter value of Y:";
cin>>y;
}
void print(){
cout<< "(" << x << "," << y <<")";
}
}; 40
void main()
{
Point p1,p2,p3={10,6},p4; //
All seem fine
p1.init();
p1.print();
p2.init(2,3);
p2.print();
p3.print();
p4.input();
p4.print();
}
//Output…
(0,0)
(2,3)
(10,6)
Enter value of X: 44
Enter value of Y:55
(44,55)

41. STUDENT’S HOME WORK
Sales Data Analysis
41

42. Programming Example: Sales Data Analysis
• 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
42

43. Programming Example: Output Format
----------- 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)
43

44. Programming Example: Output Format (cont'd.)
• 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
44

45. Programming Example: 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
45

46. Programming Example: Problem Analysis
• Main components for each salesperson:
– ID
– Quarterly sales amount
– Total annual sales amount
• Use a struct to group the components
• Six people: array of size six
• Program requires total sales for each
quarter
– Use array of size four to store the data
46

47. Programming Example: Problem Analysis
(cont'd.)
47

48. Programming Example: Problem Analysis
(cont'd.)
• Read the salespeople IDs into the array
salesPersonList
• Initialize the quarterly sales and total sales for each
salesperson to 0
48

49. Programming Example: Problem Analysis
(cont'd.)
• For each entry in the file with 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
49

50. Programming Example: Problem Analysis
(cont'd.)
• Once the sales data file is processed:
– Calculate the total sale by salesperson
– Calculate the total sale by quarter
– Print the report
50

51. Programming Example: Algorithm Design
• Translates into the following algorithm:
– Initialize the array salesPersonList
– Process the sales data
– Calculate the total sale by salesperson
– Calculate the total sale by quarter
– Print the report
– Calculate and print maximum sale by salesperson
– Calculate and print maximum sale by quarter
51

52. Programming Example: Main Algorithm
• 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
52

53. Programming Example: Main Algorithm (cont'd.)
• 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
53

54. Programming Example: Main Algorithm (cont'd.)
• Open the output file
• Output data to two decimal places
• Process sales data
– Call the function getData
• Calculate the total sale by quarter by calling the function
saleByQuarter
• Calculate the total sale by salesperson by calling the
function totalSaleByPerson
54

55. Programming Example: Main Algorithm (cont'd.)
• 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
maxSaleByPerson
• Find and print the quarter producing the maximum sale for
the year by calling maxSaleByQuarter
• Close files
55

56. Summary
• struct: collection of a fixed number of
components
• Components can be of different types
– Called members
– Accessed by name
• struct is a reserved word
• No memory is allocated for a struct
– Memory when variables are declared
56

57. Summary (cont'd.)
• Dot (.) operator: member access operator
– Used to access members of a struct
• The only built-in operations on a struct are the assignment
and member access
• Neither arithmetic nor relational operations are allowed on
structs
• struct can be passed by value or reference
• A function can return a value of type struct
• structs can be members of other structs
57