Structures I-Computer Programming-Lecture Slides, Slides of Computer Programming

Download Structures I-Computer Programming-Lecture Slides and more Slides Computer Programming in PDF only on Docsity!

CS 1124

Lecture 17-

Winter 2011

Dec 28-30, 2011January 4-6, 2011Ghufran Ahmed

Structures

Suppose you want to store data about your favoriteperson

Are all the interesting attributes of him/her of the samedata type?

What if you use arrays? How many needed?

Structure is a

compound

data type

Compound = Fancy word for:

can have various data

types stored in it

A single structure needed to store your favorite person

If you have a bunch of favorites, you just need what?

An array of structures

Structures

struct

Favorite

char

name[40];

char

address[70];

int

weight;

double

height;

//don’t forget semicolon as

it is a statement

Favorite

is

structure name

(also called tag)

height,

name

etc. are its

members

Now we can declare variables of this datatype:

favorite

person1,

person2;

Could also have done

struct

favorite{…}person1,

person2;//multiple

variables

struct{…}person;

//can’t

declare

new

variables

ahead

Structure

typedef struct TagName{

// data members

char name[40];char address[70];int weight; double height;

}TypeName;typedef struct Favorite{

char name[40];char address[70];int weight; double height;

}Favorite;

Initialization of Members

struct Favorite{

char name[40];char address[100];int weight;double height;

};Favorite person = {"Sherlock", "221 Baker Street", 150, 6.2}; •

What if we do:

Favorite person = {"Sherlock"};cout<<person.name<<person.address<<person.weight<<

person.height<<endl;

The rest automatically initialized to zero or null

An Example

#include

<iostream.h>

#include

typedef

struct

Favorite

char

name[40];

char

address[100];

int weight;double

height;

} Favorite;int main(){

Favorite

person;

strcpy(person.name, "Ali");strcpy(person.address,"LUMS,

Pakistan“);

person.weight

person.height

cout<<person.name<<endl<<person.address<<endl<<person.weight<<

endl<<person.height;

return 0;

} •

Note placement of structure (global). Can also be placed inside main().

Better here if other functions use it

Functions Passing and Returning Structures

-^

Passed by value. Original unaffected. Overhead if large structure

#include <iostream.h>typedef struct TravelTime{

int

hours;

int

mins;

} TravelTime;TravelTime sum(TravelTime t1, TravelTime t2);void main(){

TravelTime day1 = {5,

45};//5 hrs, 45 mins

TravelTime day2 = {4,

55};//4 hrs, 55 mins

TravelTime

trip = sum(day1, day2);

cout<<"Two-day total: "<<trip.hours<<" hours, "

<<trip.mins<<" minutes\n";

} TravelTime sum(TravelTime t1, TravelTime t2){

TravelTime

total;

total.mins = (t1.mins + t2.mins) % 60;total.hours = t1.hours + t2.hours + (t1.mins +

t2.mins)/60;

return total; }

Output:

Two-day

total:

hours,

minutes

-^

How to pass an array by value?

Assigning Structures

Can assign one structure to another of the same type

Memberwise Assignment

takes place, even if array

#include <iostream.h>struct SType{

int a, b;

};int main(){

SType svar1, svar2;svar1.a = svar1.b = 10;svar2.a = svar2.b = 20;cout << svar1.a << ' ' << svar1.b<<endl;cout << svar2.a << ' ' << svar2.b<<endl;svar2 = svar1; // assign structurescout << svar1.a << ' ' << svar1.b<<endl;cout << svar2.a << ' ' << svar2.b<<endl;return 0;

Output: 10 10 20 20 10 10 10 10

Pointers to Structures

Can declare a pointer to a struct just as we do for others typedef struct SType1{ int a, b;}SType;SType svar1;SType1 *ptr; //ptr is

a pointer to struct stype

We can now access members with another operator too, if we usethe pointer ptr = &svar1;ptr->a = 1; //Arrow operatorptr->b = 2;cout<<ptr->a;cout<<ptr->b;cout<<svar1.a;cout<<svar1.b; What does

*ptr

give us? Takes us to the structure. Hence,

ptr->a

is equivalent to

(*ptr).a

Pointers to Structures

#include

<iostream.h>

typedef

struct

Inflatable

char

name[20];

float

volume;

double

price;

Inflatable;

int

main()

Inflatable dinghy;Inflatable

*ps

&dinghy;

cin>>ps->name;cin>>(ps).volume;cin>>ps->price;cout<<(ps).name<<endl;cout<<ps->volume<<endl;cout<<dinghy.price<<endl;

return

Functions Receiving and Returning References to Structures

#include <iostream.h>typedef struct MyStruct{

int a;int b; };MyStruct & f(MyStruct &var);int main(){

MyStruct x, y;x.a = 10; x.b = 20;cout << "Original x.a and x.b: ";cout << x.a << ' ' << x.b << '\n';//10, 20y = f(x);//assigning one struct to the othercout << "Modified x.a and x.b: ";cout << x.a << ' ' << x.b << '\n';//100, 1cout << "Modified y.a and y.b: ";cout << y.a << ' ' << y.b << '\n';//100, 1return 0; } MyStruct & f(MyStruct &var){ var.a = var.a * var.a;

var.b = var.b / var.b;return var; }

Dynamic Structures

-^

Allocated memory at run time

-^

Format same as always

#include <iostream.h>#include

typedef struct Inflatable{

char name[20];float volume;double price;

} Inflatable;void main(){

Inflatable *p = new Inflatable;gets(p->name);cin >> p->volume;cin >> p->price;

Arrays and Pointers within Structures

A struct member can be of any valid data type

struct AStructure{

int nums[10][10]; // 10 x 10 array of intsfloat b;

} var; •

To access

nums[3][7]

, do

var.nums[3][7]

A struct can have a pointer to itself as its member

struct Recursive{

int a;float b;Recursive *p;

} var; •

A very useful device. Commonly used in linked data structures

Structures within Structures (

nested

structs)

typedef struct Addr{

char name[40];char street[40];char city[40];int postcode;

}Addr;typedef struct Emp{

Addr address;//

address has datatype

struct addr

float wage;

} Emp;Emp worker; •

How to access

postcode

member of structure variable

worker

worker.address.postcode

What if

addr

*address;

worker.address->postcode = 54700;

We can then also do

worker.address = new addr;

Can end up with

student.quarter.course.grade