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CSCE 110PROGRAMMING FUNDAMENTALS

WITH C++

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Part 11. The Struct Data Type

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The Struct Data Type

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The Struct Data Type

What are Structs ?Definition & Declaration Accessing Members of a Struct Initializing a Struct VariableCompound Structs Structs as Operands & Arguments Pointers to Structs

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1. What are structs?

Structs are linear Data Structures.Unlike the array, components

(members) can be of different types.

stringint

longint

int

Member 1Member 2

Member n

One structchar

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(a) Define a struct type:struct <struct type>{

<type 1> <member 1>;<type 2> <member 2>;

……<type n> <member n>;

};

(b) Declare variables of that type:

<struct type> <var1> <var2> .. ;

2. Definition & Declaration

Required ;

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Example

// Definition of struct employeestruct employee{

string id;string name;char gender;int numDepend;money rate;money totWages;

};employee engineer , assistant;

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3. Accessing Members of a structMembers are accessed using the

member access operator, a period (.) For struct variable s and member

variable m, to access m you would use:s.m

Can use C++ operators and operations on struct members

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Accessing Members of a struct

engineer.id = “1234”;engineer.name = “Heba Ahmed”;engineer.gender = ‘F’;engineer.numDepend = 0;engineer.rate = 6.00;engineer.totWages += engineer.rate * 40.0;

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What you can do with a whole struct

Assign a struct to another struct with exactly the same structure (copy)

Pass a struct to a function by value or by reference

Return a struct as a function type

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BUT you cannot

Input or output a whole structDo arithmetic with whole structsCompare two whole structsThe above operations can only be

done on individual members of structs

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4. Initializing a Struct Variable Members can be initialized at the time a

structure variable is created using a constructor

A constructor is a special function that can be a member of a structure

It is normally written inside the structdeclaration

Its purpose is to initialize the structure’s data members

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Initializing using a Constructor Unlike most functions, a constructor is not

called; instead, it is automatically invoked when a structure variable is created

The constructor name must be the same as the structure Type name

The constructor must have no return type

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Initializing using a ConstructorExample:struct Dimensions{int length,

width,height;

// Constructor Dimensions(int L, int W, int H){length = L; width = W; height = H;}

};Usage: Dimensions box(12, 6, 3);

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5. Compound structs:Structs with Array Members// Arrays can be fields of structs, e.g.

struct studentRecord {string name;string id;float grade [10];float GPA;

};studentRecord student;student.grade[3] = 3.6; cin >> student.name;for( i = 0; i < 10; i++) cin >> student.grade[i];

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Structs with Struct Members

// A member of a struct may itself be a struct,e.g.struct nameType { cin >> person.address;

string first; cin >> person.phone;string middle; cin >> person.name.first;string last; cin >> person.name.last;

};struct personInfo {

nameType name;string address;string phone;

};personInfo person;

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Structs with Struct Members

struct point{ double x, y;};

point P;struct line{

point p1, p2;};

line L;struct triangle{

point p1, p2, p3;};

triangle T;

p.x,p.y

L.p1.x,L.p1.y L.p2.x,L.p2.y

T.p1.x,T.p1.y

T.p2.x,T.p2.y T.p3.x,T.p3.y

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Arrays of Structs

// A struct may be an element of an // array,e.g.personInfo staff [100];cout << staff [i].address;cout << staff [i].name.first;for( i = 0; i < N; i++) {

cout << staff [i].phone;cout << staff [i].name.family;

}

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6. Structs as Operands and Arguments

Arithmetic and other operations can be done struct members

Process entire struct using programmer defined functions

Often better to pass an entire structure rather than individual elements

struct copies:person = staff [6];

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Passing struct as an Argument

Grading program example Keep track of students grades Prior to our learning structs we needed

to store each item into a single variableGroup all related student items together Pass struct by const reference if you do

not want changes made

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Example(1): Grading Program

// FILE: StudentStat.h

struct studentStat{

string name;int scores[3];float average;char grade;

};

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PrintStats.cpp

// File: printStats.cpp// Prints the exam statistics

// Pre: The members of the struct variable// student are assigned values.// Post: Each member of student is displayed.

void printStats(const studentStat student) {

cout << "Exam scores for " << student. name << ": "

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PrintStats.cpp

cout << student.scores[0] << ' ' <<student.scores[1]<< ' ' <<

student.scores[2] << endl;cout << "Average score: " <<

student.average << endl;cout << "Letter grade : " <<

student.grade << endl;}

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Example(2): ReadEmp.cpp

// File: ReadEmp.cpp// Reads one employee record into oneemployee

#include <string>#include <iostream>

// Pre: None// Post: Data are read into struct oneEmployeevoid readEmployee(employee& oneEmployee) {

cout << "Enter a name terminated by # : ";

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ReadEmp.cpp

getline(cin, oneEmployee.name, '#');cout << "Enter an id number: ";cin >> oneEmployee.id;cout << "Enter gender (F or M): ";cin >> oneEmployee.gender;cout << "Enter number of dependents: ";cin >> oneEmployee.numDepend;cout << "Enter hourly rate: ";cin >> oneEmployee.rate;

}

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7. Pointers to Structs

struct electric{

string current;int volts;

};electric *p, *q;

//p and q are pointers to a struct of type electric

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Pointers to Structs

p = new electric; Allocates storage for struct of type electric

and places address into pointer p

Use operator ( . ) to access struct members.

?

current voltsp?

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Assignments

*p.current = “AC”;*p.volts = 220;

Statements above can also be written asp ->current = “AC”;p ->volts = 220;

AC

current voltsp

220

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Struct Member Access via Pointers Form: p -> <member> Example: p -> volts

Example:cout << p->current << p-volts << endl;Output

AC220

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Copy Dynamic Structsq = new electric;

Allocates storage for struct of type electric and places address into pointer q

Copy contents of p struct to q struct*q = *p;

AC

q ->current q ->voltsq

220

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The Linked List Structure

Structs and pointers can be used to arrange dynamically allocated structures into a new structure called a linked list

Example: Consider a very long number represented as a string, e.g. πstring Long_pi = “3.14159265358979323846264338327950288419716939937510……….”;

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The Simple Linked List We can build a sequence of nodes linked by

pointers:

First node pointed to by head contains the first digit ‘3’and a next pointer to next node containing ‘.’ and so on.

Last node’s next is NULL. A cursor points to the current node. It can advance

in one way only to next node, e.g. to traverse whole list.

3 1head NULL

cursor

.

nextFirst Last

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The Node Structure

struct node // specify node structure{ char d; // digit or ‘.’

node *next; // pointer to next node };node *head, *cursor , *p; // pointers to nodes

d

next

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Code segment// Create first nodep = new node;p->d = Long_pi[0]; p-> next = NULL;head = cursor = p;

//Create rest of nodesfor (i = 1; i < Long_pi.length(); i++){

p = new node; p->d = Long_pi[i]; p->next = NULL;cursor->next = p;cursor = cursor->next;

}