Pf cs102 programming-10 [structs]

Records (structs)

CS103- Computer Programming

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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.

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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.

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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.

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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 identifierdefines a memberof the structure.

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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 ofdifferent array types.

The “StudentInfo” structure has 4 membersof different types.

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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 structuretypes as members.

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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 Student2Name

Id Gender

Dept

Name

Id Gender

Dept

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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

Records (structs)

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

• Syntax:

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Records (structs) (cont'd.)

• A struct is a definition, not a declaration

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Records (structs) (cont'd.)

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Accessing struct Members

• The syntax for accessing a struct member is:

• The dot (.) is an operator, called the member access operator

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Accessing struct Members (cont'd.)

• To initialize the members of newStudent:newStudent.GPA = 0.0;newStudent.firstName = "John";newStudent.lastName = "Brown";

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• More examples:cin >> newStudent.firstName;cin >> newStudent.testScore >> newStudent.programmingScore;

score = (newStudent.testScore + newStudent.programmingScore) / 2;

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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';

elsenewStudent.courseGrade = 'F';

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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";}

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Example Conti…

Enter title: AlienEnter year: 1979My favorite movie is:2001 A Space Odyssey (1968)And yours is:Alien (1979)

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

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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

Comparison (Relational Operators)

• Compare struct variables member-wise– No aggregate relational operations allowed

• To compare the values of student and newStudent:

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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

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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 struct23

Arrays versus structs

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Arrays in structs

• Two key items are associated with a list: – Values (elements)– Length of the list

• Define a struct containing both items:

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Arrays in structs (cont'd.)

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Arrays in structs (cont'd.)

structs in Arrays

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structs in Arrays (cont’d.)

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structs in Arrays (cont’d.)

structs within a struct

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versus

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

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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 (->)

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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;}

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Example Output…

Enter title: Invasion of the body snatchersEnter year: 1978You have entered:Invasion of the body snatchers (1978)

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Example …

pmovie->title is equivalent to (*pmovie).title

*pmovie.title is equivalent to *(pmovie.title)

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Pointers & Structs

Expression What is evaluated Equivalenta.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)

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Structs & File Handling

• A file may be read record by record.

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COMPLETE EXAMPLE OF POINT

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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 <<")";}};

void main(){Point p1,p2,p3={10,6},p4; // All seem finep1.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: 44Enter value of Y:55(44,55)

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STUDENT’S HOME WORKSales Data Analysis

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

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Programming Example: Output Format----------- Annual Sales Report -------------

ID QT1 QT2 QT3 QT4 Total______________________________________________________________12345 1892.00 0.00 494.00 322.00 2708.0032214 343.00 892.00 9023.00 0.00 10258.0023422 1395.00 1901.00 0.00 0.00 3296.0057373 893.00 892.00 8834.00 0.00 10619.0035864 2882.00 1221.00 0.00 1223.00 5326.0054654 893.00 0.00 392.00 3420.00 4705.00Total 8298.00 4906.00 18743.00 4965.00

Max Sale by SalesPerson: ID = 57373, Amount = $10619.00Max 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: 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

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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

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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

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Programming Example: Problem Analysis (cont'd.)

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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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• 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

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• Once the sales data file is processed:– Calculate the total sale by salesperson– Calculate the total sale by quarter– Print the report

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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

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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

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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

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• 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

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• 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

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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

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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

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Data & Analytics

Pf cs102 programming-10 [structs]