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1/18

ESC101NFundamentals of Computing

Arnab Bhattacharya

[email protected]

Indian Institute of Technology, Kanpurhttp://www.iitk.ac.in/esc101/

1st

semester, 2010-11

Tue, Wed, Fri 0800-0900 at L7

Arnab Bhattacharya ([email protected]) ESC101N 2010 I 1 / 14
http://localhost/var/www/apps/conversion/tmp/scratch_6/[email protected]://www.iitk.ac.in/esc101/http://www.iitk.ac.in/esc101/http://localhost/var/www/apps/conversion/tmp/scratch_6/[email protected]://find/http://goback/


2/18

Structures

Structuresare customized data typesIt is declared using the keyword struct

struct Point{

double x ;

double y ;

};

struct Point is a structure having two variables x and yVariables in a structure are called membersA variable of the type structure can be defined using

struct P oi nt p ;

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3/18

Structures

Structuresare customized data typesIt is declared using the keyword struct

struct Point{

double x ;

double y ;

};

struct Point is a structure having two variables x and yVariables in a structure are called membersA variable of the type structure can be defined using

struct P oi nt p ;

A structure type can be explicitly defined using typedeft y pe d ef s t ru c t P o in t p oi n t ;

point becomes an alias for struct PointA structure variable can then simply be defined as

p oi nt s ;

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4/18

Members

Structures can be initialized during declaration

po int p = {4.0 , -3.0};

By default, they are initialized to 0 (or \0)

Same as array

Its members can be explicitly assigned values

. notation to access membersstructure variable.member name

p .x = 4.0;

p .y = -3.0;

Members behave just like ordinary variablesSize of a structure is the combined size of its members

Example: Size of point is 8 + 8 = 16 bytes

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5/18

Functions returning structures

Since structures are variables, a function can return them

p oi nt c o py _p oi n t ( p oi nt s )

{p oi nt p ;

p . x = s . x ;

p . y = s . y ;

return p ;

}

This can also be used to create structures

q = f (9.0 , -3.0) ;

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{p oi nt p ;

p . x = s . x ;

p . y = s . y ;

return p ;

}


q = f (9.0 , -3.0) ;

Copying can also be done simply by

q = p ;A structure is just a variable

Different from array

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7/18




{p oi nt p ;

p . x = s . x ;

p . y = s . y ;

return p ;

}


q = f (9.0 , -3.0) ;

Copying can also be done simply by

q = p ;

A structure is just a variableDifferent from array

Structures cannot be compared

if ( q = = p ) // e rr or

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8/18

Passing structures to functions

Since structures are variables, they can be passed to functions

Modifying the elements of a structure inside a function is temporary

void m o di f y ( p o in t p , double c , double d )

{

p . x = c ;

p . y = d ;

}

The following code prints 5.0 and 3.0

po int q = {5.0 , -3.0};

modify (q , 9.0 , 1.0) ;

p ri nt f ( % l f % lf \ n , q .x , q . y );

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9/18

Pointers to structures

A pointer to a structure can be defined

p oi nt * ptr , p ;

ptr = & p;

When a pointer to structure is passed to a function, modifying theelements of the structure inside the function becomes permanent

void m o di f y ( p o in t * p , double c , double d )

{

p - > x = c ;

p - > y = d ;

}


po int q = {5.0 , -3.0};

modify (& q , 9.0 , 1.0) ;


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10/18

Pointers to structures

A pointer to a structure can be defined

p oi nt * ptr , p ;

ptr = & p;

When a pointer to structure is passed to a function, modifying theelements of the structure inside the function becomes permanent

void m o di f y ( p o in t * p , double c , double d )

{

p - > x = c ;

p - > y = d ;

}


po int q = {5.0 , -3.0};

modify (& q , 9.0 , 1.0) ;


-> notation to access members using pointersstructure pointer->member name

ptr->x is same as (*ptr).xArnab Bhattacharya ([email protected]) ESC101N 2010 I 6 / 14
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11/18

Structure operations I

# i n c l u d e < s t d i o . h ># i n c l u d e < m a t h . h >

struct Point

{double x ;double y ;

}; / / d e fi n in g a s t ru c tu r e

t y p ed e f s t r uc t P o in t p o i nt ; / / d e fi n in g a n ew t yp e u si ng s t ru c tu r e

p o in t n e w _ po i n t ( double c , double d ) / / s t ru c tu r e a s r e tu rn v al ue{

p oi nt p ;

p . x = c ;p . y = d ;

return p ;}

double d i st a nc e ( p oi nt a , p oi nt b ) / / s t ru c tu r e a s p a ra m et e r

{double d = 0.0;

d = s qr t( po w( a. x - b .x , 2) + p ow ( a. y - b .y , 2) );

return d ;}

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12/18

Structure operations II

void m o d i fy _ w r on g ( p o i n t p , double c , double d ){

p . x = c ; / / m o di f yi n g m e mb e rs i ns i de f u nc t io n i s t e mp o ra r y

p . y = d ;}

void m o d i fy _ p o i nt e r ( p o i nt * p , double c , double d ){

p -> x = c ; / / m o di f yi n g m e mb e rs u si ng s t ru c tu r e p o in t er i s p e rm a ne n tp -> y = d ; / / - > n ot a ti o n

}

in t m a i n ( ){

struct P oi nt p , q ; / / d e c la r i ng u s in g s t r u ct u r ep oi nt s ; / / d e cl a ri n g u si ng t yp ep oi nt t = { 9. 0 , - 5. 0} ; / / i n i t ia l i z in g d u r in g d e c la r a t io n double d ;p o in t * p t r ;

p r in t f (" % lf % l f \n " , p . x , p . y ); / / b y d ef au lt , v al u es a re 0

q .x = 4 .0 ; / / a c ce s si n g o r m o di f yi n g t he m e mb e rs i n a s t ru c tu r eq .y = - 3. 0; / / . n o ta ti o n

d = d is ta nc e (p , q ) ;p r in t f (" D i st a nc e = % l f \n " , d ) ;

// p = {9.0 , -5.0 }; // e rr or

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Structure operations III

/ / p ri nt f ( "% l f % l f \n " , p . x , p . y );

p = n e w_ p oi n t (7 .0 , - 1. 0) ;

p r in t f (" % lf % l f \n " , p . x , p . y );

m od i f y_ w r on g (q , 7. 0 , -1 .0 ) ;p r in t f (" % lf % l f \n " , q . x , q . y );

p tr = & p;m o di f y _ p oi n t e r ( pt r , 2. 0 , -5 .0 ) ;p r in t f (" % lf % l f \t % lf % l f \n " , p . x , p . y , p tr - > x , p tr - > y ) ;

p ri nt f (" S iz e of p i s % d , s iz e o f p tr i s % d \ n ", sizeof ( p ) , sizeof ( p t r ) ) ;

// if (q == p) // error

/ / p r in tf ( " E q ua l s t r uc t ur e s \ n ") ;

}

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Nested structures

A structure can have another structure as its member

t y pe d ef s t ru c t Line

{p oi nt p ;

p oi nt q ;

} line ;

Note: typedef definitions can be combined equivalent to

struct Line

{

p oi nt p ;

p oi nt q ;

};

t y pe d ef s t ru c t L in e l in e ;

Value x of point p of variable l of type line can be accessed as:l.p.x

The . operator has left-to-right associativity

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Array of structures

An array of structures can be simply defined as

p o in t t [ 3 ];

Each individual structure is accessed as t[0], etc.

A member of a structure is accessed as t[i].x, etc.

All operations allowed on normal arrays are allowed on array of

structures

It is equivalent to a pointer to structure

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16/18

Array of structures

# i n c l u d e < s t d i o . h >

t y p ed e f s t r uc t Point{

double x ;double y ;

} p oi nt ;

in t m a i n ( ){

p o in t t [ 3 ] ;int i ;

for ( i = 0; i < 3; i ++){

t [i ]. x = i ;t [ i ] . y = 2 * i ;p ri n tf ( " % lf % l f \n " , t [ i ]. x , t [ i ]. y ) ;

}}


P i i
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17/18

Pointer in a structure

A structure can have a pointer as its member

t y pe d ef s t ru c t Student

{int roll;

char * n a m e ;

} s tu de nt ;

Declaring a variable of type student just declares the pointer name

it does not allocate space for its tu de nt s ;

s t rc a t ( s . na me , . ) ; // e rr or

Memory for name has to be allocated explicitly using malloc

s .name = ( char * ) m al lo c ( 30 * sizeof ( char ) ) ;

10 14

student

...

80

name[0]roll name


P i i
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18/18

Pointer in a structure

# i n c l u d e < s t d i o . h ># i n c l u d e < s t r i n g . h ># i n c l u d e < s t d l i b . h >

t y p ed e f s t r uc t Student{

int r o l l ;char * n a m e ;

} s tu d en t ;

in t m a i n ( ){

s t ud en t s ;

s . na me = ( char * ) m a l lo c ( 3 0 * sizeof ( char ) ) ;

s c an f ( " % d % s " , & s . r ol l , s . n a me ) ;

p r in t f (" % d % s \ n" , s . ro ll , s . n am e ) ;

s t r ca t ( s . n am e , " A " ) ;

p r in t f (" % d % s \ n" , s . ro ll , s . n am e ) ;

f r e e ( s . n a m e ) ;}

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