Chapter 8 Structure in C

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Structure in C


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Important Question

Explain Structure with example

Explain Union with example.

State diff between Array and Structure

State diff between Structure and Union


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Topic Covered

Introduction

Declaration

Accessing

Initialization

Copying & Comparing

typedef and its use in Structure Declaration

Nesting of Structure


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Topic Covered

Arrays of Structure

Initializing Arrays of Structure

Arrays within Structure

Structures and Pointers

Structures & Functions


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Introduction

Arrays require that all elements be of the same datatype.

Many times it is necessary to group information ofdifferent data types.

An example is a materials list for a product. The listtypically includes a name for each item, a part number,dimensions, weight, and cost.

C and C++ support data structures that can store

combinations of character, integer floating point andenumerated type data. They are called a structs.


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Structure

Structure is user defined data type which is used to store

heterogeneous data under unique name.

A structure is a collection of variables under a single

name. These variables can be of different types, and eachhas a name which is used to select it from the structure.

A structure is a convenient way of grouping together

pieces of related information.

Keyword 'struct' is used to declare structure.

A single structwould store the data for one object. An

array ofstructs would store the data for several objects.

The variables which are declared inside the structure are

called as 'members of structure'.


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General Form

Struct


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Explanation

The structure_tag_name is the name of the structure

The structure_variables are the list of variable names

separated by commas

Each of these structure_variable name is a structure oftype structure_tag_name

Each member_name declared within the braces is called a

member or structure element.


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Declaration

There are three different ways to declare

and/or define structure

Variable structure

Tagged structure

Type-defined structure


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Variable Structure

struct

{

member_list}variable_identifie;

struct

{

int x;int y;

}a;


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Tagged Structure

The tag name is referred to in subsequent declarations of

variables of the type so defined.

Each such declaration MUST include the keyword struct

AND the name of the user-defined structure type AND the

variable name(s).

struct tag_name

{ member_list

}variable_identifie;

struct s1

{int x;

int y;

}a;


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Where Declare???

The proper place for structure declarations is in the

global area of the program before main()

This puts them within the scope of the entire program

and is mandatory if the structure is to shared by function.


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Accessing

In C program for accessing the elements of structure

use dot operator('.').

For accessing element you need to the structure

variable.The general format is :

.;

It has the same precedence as () and [], which is higher

than that of any unary and binary operator. Like () and [], it associates from Left to Right.


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Demo


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Initialization of Structure

A structure can be initialized in much the

same way as any other data type.

This consists of assigning some constants to

the members of the structures.

Default Value

For integer and float : 0 (zero)

For char and string type : \0


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General Intializing Structre

struct

{

;

;

.

.

}={constant1, constant2,..>

Or

struct

= {constant1, constant2,..}


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DEMO


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ARRAY VS STRUCTURE


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Union

Union is user defined data type used to stored data under

unique variable name at single memory location.

Union is similar to that of stucture.

Syntax of union is similar to stucture. But the major difference between structure and union is

'storage.'

In structures, each member has its own storage location,

whereas all the members of union use the same location. Union contains many members of different types, it can

handle only one member at a time.

To declare union data type, 'union' keyword is used.


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Declaration

Syntax:

union union_name

{

element 1;

element 2; element 3;

}union_variable;

Example:

union techno

{int comp_id;

char nm;

float sal;

}tch;


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Memory Allocation for Union


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Accessing


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DEMO


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Output


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Difference Between Union and Structure


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Memory Required for Structure

There is difference in memory allocation between union

and structure as suggested in above example.

The amount of memory required to store a structure

variables is the sum of memory size of all members.


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Memory Required for Union

But, the memory required to store a union variable is the

memory required for largest element of an union.


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Structure Vs Union

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Chapter 8 Structure in C