structure and union from c programming language.ppt

Objective
 Definition of Structure
 Declaring structure variable
 Accessing Structure members
 Structure initialization
 Array of structure
 Array within structure
 Structure within structure
 Union
 Union vs. Structure

Definition of structure
1. A collection of variables that are functionally related to each
other.
2. Each variable that is a member of the structure has a specific
type.
3. Different members of the structure may have either the same
or different types. Cf. the elements of an array, which must all
be of one type.
4. A structure is a derived data type, constructed from two or
more objects of one or more individual types.
5. The entire structure may bear a name.
6. Each member of the structure must [also] have a name.
7. The scope of the name of a structure member is limited to the
structure itself and also to any variable declared to be of the
structure's type.

Continue…
8. THEREFORE, different structures may contain members
having the same name; these may be of the same or of
different types.
9. A self-referential structure contains a member which is a
pointer to the same structure type.
10. Declaration of the structure merely defines the new data
type; space is NOT reserved in memory as a result of the
declaration.
(However, declaration of the structure does define how
much memory is needed to store each variable
subsequently declared to be of the type of the defined
structure.)

Example
Struct book
{
char name;
float price;
int page;
};
name
price
page
Memory representation
name price page
Char float int

Structure declaration -1
struct nameOfThisStructureType
{
typeOfFirstMember nameOfFirstMember;
typeOfSecondMember nameOfSecondMember;
typeOfThirdMember nameOfThirdMember;
. . .
};
Struct nameOfThisStructureType variable1OfThisStructureType,
variable2ofThisStructureType, … ;
Example
Struct book
{
char name;
float price;
int page;
};
Struct book b1,b2,b3;

struct nameOfThisStructureType
{
. . .
} variable1OfThisStructureType, variable2OfThisStructureType, . . .;
Example
Struct book
{
char name;
float price;
int page;
} b1,b2,b3;

struct /* NO NAME ASSIGNED TO THE TYPE */
{
. . .
} variable1OfThisStructureType, variable2OfThisStructureType, . . .;
Example
Struct
{
char name;
float price;
int page;
} b1,b2,b3;

Accessing Structure members
To access structure members we have to (.)operator.
variable1OfTheStructureType.nameOfTheMember
Example
b1.page
b2.price

Structure initialization
A structure can be initialize by the following way,
Watch this example.
Example
struct book
{
char name;
float price;
int pages;
};
struct book b1={‘B’, 130.00, 550 }; //structure initialization

Simple structure program
#include<stdio.h>
void main()
{
struct book
{
char name;
float price;
int pages;
};
struct book b1={‘B’, 130.00, 550 };
printf(“n book name is:%c”,b1.name);
printf(“n book price is: %f”,b1.price);
printf(“n book pages are: %d”,b1.pages);
}

Array of structure
Array of structure is possible in c language. If
you declare a array of structure then the
variables of the structure type will be stored in
continuous memory locations. An example of
declaring an array of structure is given below.
struct book
{
char name;
float price;
int pages;
};
struct book b[100]; //declaration of array of structure

Sample program of array of structure
#include<stdio.h>
void main()
{
struct book
{
char name;
float price;
int pages;
};
struct book b[100];
int i;
for(i=0;i<=99;i++)
{
printf(“n Enter name, price and pages”);
scanf(“%c %f %d”, &b [i].name,&b[i].price,&b[i].pages);
}
for(i=0;i<=99;i++)
printf(“n %c %f %d”, b[i].name,b[i].price,b[i].pages);
}

Array within structure
Array can exist as a member of structure. A
simple example is given below.
struct book
{
char name[100]; //Array within structure
float price;
int pages;
};
struct book b1;

Structure within structure
A structure itself can be member of another structure.
This is given in the following example.
Struct employee
{
char name[100];
char department[20];
struct
{
int dearness;
int house_rent;
int city;
}allowance;
}emp1,emp2,emp3;

Union
What is union?
1. Like a structure, a union is also a derived data type.
2. The members of a union share a single storage space.
3. Only ONE member of each union can be referenced t
a time.
4. Amount of space allocated for storage is the amount
needed for the largest member of the union.

Example of union
union book
{
char name;
float price;
int pages;
};
This will take memory space of 4 bytes, since
price(datatype is float which is of 4 bytes) is the
largest member in this union. This 4 byte is shared by
all the members in the union. Only 1 member of this
union can be referenced at a time

Union vs. Structure
1. struct keyword required to declare a structure, union
keyword required to declare a union.
2. Every structure member is allocated memory when a
structure variable is defined. whereas in union the memory
equivalent to largest item that is allocated commonly for all
members.
3. In union only one member can assign values at a time. But
in structure all the members can assign at a time.
4. memory can be allocated dynamically in structure, where as
in union can not be allocated dynamically.
5. In structures value assigned to one member cannot cause
the change in other members ,where as in union it cause
change in values of other members.
6. Self referential structure is possible, But self referential
union is not possible.

structure and union from c programming language.ppt

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