INTRO TO STRUCTS IN C++

A LECTURE FOR THE C++ COURSE

Each slide may have its own narration in an audio file. �For the explanation of any slide, click on the audio icon to start the narration.

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The Professor‘s C++Course by Linda W. Friedman is licensed under a �Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

WHAT IS A STRUCTURE? A RECORD

• A struct is a C++ keyword that refers to a structure. This is a collection of variables, not necessarily of the same type. These variables are called the members of the structure.
• A structure is equivalent to a record.
• A record is a collection of data items related to a single object of processing.
• More formally, a record is a finite, ordered collection of possibly heterogeneous elements, which may themselves be composite structures. The primary purpose of the record data type is to group together logically related fields. A collection of logically related record occurrences that are treated as a unit is called a file.

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RECORDS

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The record is a simple yet fundamental type of data structure. A record generally contains an identifying field (key), e.g., EMPLOYEE, a data structure of type record:

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Where do we see

• Array within a record:
• Record within record:
• Record within record within array:

STRUCTS IN C++

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• A structure enables you to define a new type that logically groups several fields (members) together.

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• Structures were more important in C (in the old days before object-oriented programming). In C++ they are more likely to be part of a class definition. In fact, a struct is almost the same as a class.

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General syntax:

struct structName {

--list of members--

};

EXAMPLES

struct point {

double x;

double y;

};

• Defining a structure is like defining a new type. Then you can declare variables of the new type:

point p1, p2, p3;

• or like this:

struct point {

double x;

double y;

} p1, p2, p3;

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Also like this:

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struct {

double x;

double y;

} p1, p2, p3;

EXAMPLES

struct point {

double x;

double y;

};

struct rectangle {

point upperLeftCorner;

point lowerRightCorner;

};

struct circle {

point center;

double radius;

};

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Also these

USING STRUCTS

One way to declare and initialize:

point p5 = {1.0, -8.3};

To access individual members, use the dot operator:

p1.x = 12.45;

p1.y = 34.56;

p2.x = 23.4 / p1.x;

p2.y = 0.98 * p1.y;

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SMALL EXAMPLE

//structs.cpp

/*illustration of use of structs for organizing data into records*/

#include <iomanip>

#include <fstream>

using namespace std;

ifstream infile ("d:in.dat");

ofstream outfile ("d:out.txt");

struct record { //struct definition

int num1;

int num2;

};

int main(){

record rec; //declaring struct variable rec

float avg;

if (!infile) //testing files

cerr << "Error: could not open input file\n";

else if (!outfile)

cerr << "Error: could not open output file\n";

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//printing headings

outfile << setw(18) << "Number 1" � << setw(15)<< "Number 2 "

<< setw(15)<< "Average\n\n";

while (infile >> rec.num1 >> rec.num2){

avg = (rec.num1 + rec.num2) /2.0;

outfile << setiosflags(ios::showpoint | ios::fixed)

<< setprecision(2) << setw(15) <<rec.num1

<< setw(15) << rec.num2

<< setw(15) << avg << endl;

}

return 0;

}

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INPUT / OUTPUT

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WHERE TO USE STRUCTS?

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What sort of programs are good candidates for using structs?

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• Employee processing Program
• Inventory processing Program
• Even student grading Program

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REVIEW

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What did we learn in this lecture? Plenty. Some terms to jog your memory:

• Structs
• Declaring a struct
• Accessing the named elements in a struct