Senem Kumova Metin STRUCTURES continues CHAPTER 9 in A Book in C.

Senem Kumova Metin

STRUCTUREScontinuesCHAPTER 9 in A

Book in C

Senem Kumova Metin

Structures in C

• A structure is – a convenient way of grouping several

pieces of related information together– a collection of variables under a single

name

Examples :

real number && imaginary number complex number ( 3+5i )

height && width && length rectangular prism

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Defining Structures/* DEFINITION OF RECTANGULAR

PRISM */struct rectangular_prism{ int height;

int width;int length;};

// name of new type??

/* DEFINITION OF STUDENT RECORD */

struct student_record{ int ID;

char name[100]; };

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Structures : Creating objects

struct complex{ int real;

int imaginary; };

// create an object

struct complex s;struct complex * p= (struct complex *)

malloc( sizeof(struct complex));

// create an array of objects

struct complex a[4];struct complex * p= (struct complex *)

malloc( sizeof(struct complex)*4);

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Structures : Accessing members of structures 1

struct complex{ int real;

int imaginary; };

struct complex s;// access members

s.real=5; s.imaginary =3;

struct complex * p= (struct complex *) malloc( sizeof(struct complex));

// access members

p->real=5; p->imaginary=3;

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Structures : Accessing members of structures 2

struct complex{ int real;

int imaginary; };

int i;struct complex a[4];struct complex * p=

(struct complex *) malloc( sizeof(struct complex)*4);

for(i=0;i<4;i++) { a[i].real=i; p[i].real=i;

a[i].imaginary=i; p[i].imaginary=i; }

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Structures : DECLARATION ALTERNATIVES

• struct record { int ID; char * name; char grade; };

struct record s1;

• struct record { int ID; char * name; char grade; } s1, s2;

• struct { int ID; char * name; char grade; } s1, s2;

• struct record { int ID; char * name; char grade; };

typedef struct record rec;

• typedef struct { int ID; char * name; char grade; } rec;

rec s1;

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Structures as Function Arguments Examples

Example1. Call by valueExample2. Call by valueExample3. Call by referenceExample4. Arrays

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Example 1 : Define functions

// A function to add two integersint sum(int a, int b){ int result= a+b;

return result; }

struct complex { int r; int i; };

// A function to add two complex numbersstruct complex sum ( struct complex a, struct

complex b ){ struct complex result;

result.r=a.r+b.r;result.i=a.i+b.i;return result; }

// A function to print out a complex numbervoid my_print ( struct complex a){ printf(“%d+%di\n”, a.r, a.i ); }

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Example 1 : Define main()

// Structure definitionstruct complex { int r; int i; } ;

// function prototypesstruct complex sum ( struct complex a, struct complex b );void my_print ( struct complex a);

main(){ struct complex e1={2,3};

struct complex e2 ={1,2};struct complex e3;

my_print(e1);my_print(e2);e3=sum(e1, e2);my_print(e3); }

void my_print ( struct complex a){ printf(“%d+%di\n”, a.r, a.i );}

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Example 2 • Define a date structure

day - month – year

• Define a function to find the next dayTODAY NEXT DAY

– 5 – 1 – 2009 6 – 1 - 2009– 30 - 1 - 2009 1 - 2 - 2009– 30 - 12 – 2009 1 – 1 - 2010

• In main create an object of today and call function to find next day

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Example 2 typedef struct { int day; int month; int year; } date ; // structure

definition

date calculate ( date d ) // function definition{ date n;

if( d.day==30) if(d.month==12) { n.day=1; n.month=1;

n.year=d.year+1; } else { n.day=1; n.month=d.month+1;

n.year=d.year; }

else {n.day=d.day+1; n.month=d.month; n.year=d.year; } return n; }

main() // main function{ date today ={12, 10, 2005};

date next_day;next_day= calculate(today);printf(“Next day is %d.%d.%d”,

next_day.day,next_day.month,next_day.year);}

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Example 3 (Call by reference) : Define functions

// A function to increase an integersvoid increase_i (int *a){ *a=*a+1; }

typedef struct { int n; int d; } fraction; // fraction=n/d

// A function to increase a fractionvoid increase_f (fraction * a ){ a->n= a->n +a->d; }

// n/d+1 = (n+d) /d

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Example 3 (Call by reference): Define functions

// A function to swap integersvoid swap_i (int *a , int * b){ int tmp;

tmp=*a;*a=*b;*b=tmp; }

typedef struct { int n; int d; } fraction;

// A function to swap fractionsvoid swap_f (fraction *a , fraction * b){ fraction tmp;

tmp=*a;*a=*b;*b=tmp; }

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Example 3 (Call by reference): Define main()

typedef struct { int n; int d; } fraction;

void swap_f (fraction *a , fraction * b);void increase_f (fraction * a );

main(){ fraction x={3,4};

fraction y={4,5};

increase_f(&x);increase_f(&y);

swap_f(&x,&y);swap_f(&y,&x);

printf(“%d/%d\n”,x.n,x.d);printf(“%d/%d\n”,y.n,y.d); }

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Example 4 : Arrays ( Bookstore example)

• You will create Bbookstore_system

• Ask user to enter how many different books he has.

• You have to store name and total number of copies for each book.

• Ask user to enter information for each book.

• Define a function to calculate the number of books in store.

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Example 4 : Arrays

void main(){ int s, i, total;

book * array;printf("How many books do you have?");scanf("%d",&s);

array= (book *)malloc(sizeof( book)*s);

for(i=0;i<s;i++)scanf("%d",&(array[i].number));total=sum(array,s); // sum(&array[0]);

printf("total number of books %d",total); }

typedef struct{ char * name;

int number;} book;

int sum( book * a, int size){ int i; int r=0;

for (i=0;i<size;i++) r=r+a[i].number;

return r;}/* int sum( book a[], int

size){ int i; int r=0;

for (i=0;i<size;i++)

r=r+a[i].number;

return r;}

*/

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UNIONS • A union

– defines a set of alternative values that may be stored in a shared poriton of memory

– is similar to structures a collection of variables under a single name

Examples :

union int _or_float {int i; float f;};

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Example 1: UNIONS union int_or_char { char c;

int i; };

int main(){ union int_or_char test;

test.i= 83;printf("i= %d\n", test.i); // 83printf("c= %c\n", test.c); // S

test.c='A';printf("i= %d\n", test.i);printf("c= %c\n", test.c);return 0;

}

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union int_or_double{ /* to be used as an integer OR a double*/

int i; /*needs 4 bytes*/double d; /*needs 8 bytes*/ };

main(){

printf ("%d\n", sizeof(int));printf ("%d\n", sizeof(double));printf ("%d\n", sizeof(union

int_or_double));

}

Example 2: UNIONS

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Bit Fields

• The bit field is used to pack the bits.

• An int or unsigned member of a structure or union can be declared to consist of a specified number of bits. Such a member is called a bit field, and the number of associated bits is called its width. The width is at most the number of bits in a machine word.

• The compiler packs the bit fields into a minimal number of machine words

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Example : Bit Fieldsstruct Bits {

int a:2; /* 2 bit */unsigned b:4; /* 4 bits */int c:1; /* 1 bit */};

int main(){

struct Bits x;x.a=1;x.b=5; x.c=1;printf("a:%d b: %d c:%d\n", x.a , x.b, x.c); return 0;

}