Chapter 11:

Structured Data

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Introduction• An array makes it possible to access a list or table of data of the

same data type by using a single variable name. At times, however, we may want to store information of varying types, such as a string name, an integer part number, and a real price, together in one structure. A data structure that stores different types of data under a single variable name is called a record

• For example, consider preparing an employee record. Each of the individual data items listed below is an entity by itself that is referred to as a data field. Taken together, all the data fields form a single unit that is referred to as a record. In C++, a record is referred to as a structure. Name: Identification Number: Regular Pay Rate: Overtime Pay Rate:

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Combining Data into Structures• Structure: C++ construct that allows multiple variables to be

grouped together• General Format:

struct <structName>{type1 field1;type2 field2;. . .

};

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Example struct Declaration

struct Student{

int studentID;string name;

short yearInSchool;double gpa;

};

structure tag

structure members

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struct Declaration Notes

• Must have ; after closing }• struct names commonly begin with

uppercase letter• Multiple fields of same type can be in comma-

separated list:string name, address;

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Defining Variables

• struct declaration does not allocate memory or create variables

• It creates a new data type• To define variables, use structure tag as type

name:Student bill; studentID

name

yearInSchool

gpa

bill

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Accessing Structure Members

• Use the dot (.) operator to refer to members of struct variables:cin >> bill.studentID;getline(cin, bill.name);bill.gpa = 3.75;

• Member variables can be used in any manner appropriate for their data type

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Displaying a struct Variable

• To display the contents of a struct variable, must display each field separately, using the dot operator:cout << bill; // won’t workcout << bill.studentID << endl;cout << bill.name << endl;cout << bill.yearInSchool;cout << " " << bill.gpa;

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Comparing struct Variables

• Cannot compare struct variables directly:if (bill == william) // won’t work

• Instead, must compare on a field basis:if (bill.studentID ==

william.studentID) ...

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Initializing a Structure

• struct variable can be initialized when defined:Student s = {11465, "Joan", 2, 3.75};

• Can also be initialized member-by-member after definition:

s.name = "Joan";s.gpa = 3.75;

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More on Initializing a Structure• May initialize only some members:

Student bill = {14579};

• If you leave a structure member uninitialized, you must leave all members that follow it uninitialized as well!!

• Cannot skip over members:Student s = {1234, "John", , 2.83}; // illegal

• Cannot initialize in the structure declaration, since this does not allocate memory

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Excerpts From Program 11-4

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Nested Structures• A structure can contain another structure as a member:• To include a structure within a structure (Nested Structures, p. 642), we

follow the same rules for including any data type in a structure. For example, assume that a structure is to consist of a name and a date of birth, where a Date structure, has been declared as struct Date

{ int month; int day; int year;};

• A suitable definition of a structure that includes a name and a Date structure is

struct Person {

string name; Date birth; };

struct Date{

int month; int day; int year;

};struct Person{ string name; Date birth;};int main ( void ){ Person employee; employee.name = "Mary Hill"; employee.birth.month = 12; employee.birth.day = 25; employee.birth.year = 2002;

cout << employee.name << " birthdate is: “ << employee.birth.month << "/" << employee.birth.day << "/“ << employee.birth.year;

return 0;}

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Arrays of Structures• Structures can be defined in arrays• Can be used in place of parallel arraysconst int NUM_STUDENTS = 20;Student stuList[NUM_STUDENTS];

• Individual structures accessible using subscript notation

• Fields within structures accessible using dot notation:cout << stuList[5].studentID;

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Structures as Function Arguments• Individual structure members may be passed to

a function in the same manner as any variable. • May pass members of struct variables to

functions:computeGPA(stu.gpa);

• May pass entire struct variables to functions:showData(stu);

• Can use reference parameter if function needs to modify contents of structure variable

struct Employee // declare a global type{ int id_number; double pay_rate; double hours;};double calcNet(double, double); // function prototype

int main ( void ){ Employee emp = {6782, 8.93, 40.5}; double net_pay;

net_pay = calcNet(emp.pay_rate, emp.hours); //PASS BY VALUE

cout << setw(10) << fixed << showpoint << setprecision(2); cout << "The net pay for employee " << emp.id_number << " is $" << net_pay << endl;

return 0;}double calcNet(double pay_rate, double hours) { return (pay_rate * hours); } //PASS BY VALUE

//Output:The net pay for employee 6782 is $361.66• This example passes copies of the values stored in structure members emp.pay_rate

and emp.hours to the function named calcNet( ).

struct Employee // declare a global type { int id_number; double pay_rate;

double hours; }; double calcNet(Employee); // function prototype

int main ( void ) { Employee emp = {6782, 8.93, 40.5}; double net_pay; net_pay = calcNet(emp); cout << setw(10) << fixed <<showpoint << setprecision(2); cout << "The net pay for employee " << emp.id_number << " is $" << net_pay << endl; return 0;}

double calcNet(Employee temp) { return (temp.pay_rate * temp.hours); }

• Output The net pay for employee 6782 is $361.66