stru union

8/12/2019 Stru Union

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A structure is a user defined data type. We know that arrays can be

used to represent a group of data items that belong to the same type, such as int

or float. However we cannot use an array if we want to represent a collection of

data items of different types using a single name. A structure is a convenient tool

for handling a group of logically related data items.

The syntax of structure declaration is

struct structure_name

type element !"

type element #"

$$$$$..

type element n"

%"

&n structure declaration the keyword struct appears first, this

followed by structure name. The member of structure should be enclosed

between a pair of braces and it defines one by one each ending with a semicolon.

&t can also be array of structure. There is an enclosing brace at the end of

declaration and it end with a semicolon.

We can declare structure variables as follows

struct structure_name var!,var#,$..,var n"

'or (xample)

To store the names, roll number and total mark of a student you

can declare * variables. To store this data for more than one student * separate

arrays may be declared. Another choice is to make a structure. +o memory is

allocated when a structure is declared. &t ust defines the -form of the structure.

When a variable is made then memory is allocated. This is e/uivalent to saying

that there0s no memory for -int , but when we declare an integer that is. int var"

only then memory is allocated. The structure for the above1mentioned case will

look like


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struct student

int rollno"

char name2#34"

float totalmark"

%"

We can now declare structure variables stud!, stud# as follows

struct student stud!,stud#"

Thus, the stud! and stud# are structure variables of type student. The above

structure can hold information of # students.

&t is possible to combine the declaration of structure combinationwith that of the structure variables, as shown below.

struct structure_name

type element !"

type element #"

$$$$$..

type element n"

%var!,var#,$,varn"

The following single declaration is e/uivalent to the two

declaration presented in the previous example.

struct student

int rollno"

char name2#34"

float totalmark" % stud!, stud#"

The different variable types stored in a structure are called its

members. The structure member can be accessed by using a dot 5.6 operator, so

the dot operator is known as structure member operator.


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(xample)

&n the above example stud! is a structure variable of type

student. To access the member name, we would write

stud!.name

7imilarly, stud!8s rollno and stud!8s totalmark can be accessed by writing

stud!.rollno And

stud!.totalmark

Initializing Structure Members

7tructure members can be initiali9ed at declaration. This much the same manner

as the element of an array" the initial value must appear in the order in which

they will be assigned to their corresponding structure members,enclosed inbraces and seperated by commas .The general form is

struct stucture_name var:val!,val#,val*$..%"

(xample)

;include


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printf5?nBoll number)Idnn+ame)IsnnTotel mark)

I.#fn?,stud#.rollno,stud#.name,stud#.totalmark6"

printf5?nBoll number)Idnn+ame)IsnnTotel mark)

I.#fn?,stud*.rollno,stud*.name,stud*.totalmark6"

getch56"

return J"

%

Array of structures:

&t is possible to store a structure has an array element. i.e., an array in

which each element is a structure. Kust as arrays of any basic type of variable are

allowed, so are arrays of a given type of structure. Although a structure containsmany different types, the compiler never gets to know this information because it

is hidden away inside a sealed structure capsule, so it can believe that all the

elements in the array have the same type, even though that type is itself made up

of lots of different types.

The declaration statement is given below.

struct struct_name

type element !"

type element #"

$$$$$..

type element n"

%array name2si9e4"

(xample)

struct student

int rollno"

char name2#34"

float totalmark"

% stud2!JJ4"


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&n this declaration stud is a !JJ1element array of structures.

Hence, each element of stud is a separate structure of type student. An array of

structure can be assigned initial values ust as any other array. 7o the above

structure can hold information of !JJ students.

program)

;include


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printf5?nBoll number)Idn?,stud2i4.rollno6"

printf5?+ame)Isn?,stud2i4.name6"

printf5?Totel mark)Idn?,stud2i4.totalmark6"

%

getch56"

return J"

%

Structure as structure member:

A structure can have one or more of its member as another

structure, but a structure cannot be member to itself when a structure is used as

structure member. &n such situation, the declaration of the embedded structuremust appear before the declaration of the outer structure. 'or example

;include


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printf5?(nter total number of studentsnn?6"

scanf5?Id?,Ln6"

for(i=0;i


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The real purpose of unions is to prevent memory fragmentation by

arranging for a standard si9e for data in the memory. Oy having a standard data

si9e we can guarantee that any hole left when dynamically allocated memory is

freed will always be reusable by another instance of the same type of union. This

is a natural strategy in system programming where many instances of different

kinds of variables with a related purpose and stored dynamically.

A union is declared in the same way as a structure.The syntax of

union declaration is

union union_name

type element !"

type element #"

$$$$$..

type element n"

%"

This declares a type template. Dariables are then declared as)

union union_name x,y,9"

'or example, the following code declares a union data type called

7tudent and a union variable called stud)union student

int rollno"

float totalmark"

%"

union student stud"

&t is possible to combine the declaration of union combinationwith that of the union variables, as shown below.

union union_name

type element !"

type element #"


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$$$$$..

type element n"

%var!,var#,$,varn"

The following single declaration is e/uivalent to the two

declaration presented in the previous example.

union student

int rollno"

float totalmark"

%x,y,9"

(xercise) Pompare structure and Enion

7tructure)


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Enion)

#include

#includeint main()

{

union student {

char *name;

int rollno;

float totalmark; }stud1;

// union student stud1={"shraf"!1!}; stud1.name="shraf"; $rintf("%&'&% &+,%-nname-s"!stud1.name);

stud1.rollno=1; $rintf("n0oll numer-d"!stud1.rollno);

stud1.totalmark=23.45;


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$rintf("ntotalmark-f"!stud1.totalmark);

6hat is the main difference et7een %&0'8&'0 and '+9:

All the members of the structure can be accessedatonce,where as in an union only one member can be usedat a time.Another important difference is in the size allocatedto astructure and an union.for eg:

struct example{ int integer; float floating_numbers;}the size allocated here is sizeofint!"sizeoffloat!;where as in an unionunion example{ int integer;

float floating_numbers;}size allocated is the size of the highest member.so size is#sizeoffloat!;

stru union

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