Structure
and Union
Structure: Structures
are also one of the derived data types in C. It is the collection of dissimilar
data types like an int, float and char under a single name. So whenever you
require putting dissimilar data type together you can use a structure.
Structure is a collection of Heterogeneous
data type. All the elements of structure stored at contiguous memory locations.
It is Collection of variables under a single name.
You can use variables of any type inside a structure. Each separate variable is
called a member.
Definition
A Structure is collection of dissimilar
(heterogeneous) data elements stored at contiguous memory location.
struct
keyword is used for creating Structure.
Syntax:
struct structure name
{
datatype1 member1;
datatype2 member2;
};
E.g. A
Student could have name, roll no and marks etc.
struct student
{
char name[10];
int roll_no;
int class;
};
Declaring a structure
·
Like any other variables in C , a structure has to be declared,
before it can used.
·
A structure can be defined in C by the keyword struct followed
by its name and a body enclosed in curly braces.
·
The body structure contains the definition of its members
and each member must have a name. The declaration ends by a semicolon. It is
also called structure template.
struct
<name>
{
data_type
variable_name1;
data_type
variable_name2 ;
.
.
data_type
variable_name n;
};
Where
struct is the keyword.
“name”
is the name of the structure and “variable_name” is the name of the member
variable and the “data_type” is the data type of the member variable.
Let
us now define the c structure to describe the information about the student,
struct
student
{
char
name [20];
int roll;
char
class [5];
};
The
declaration means that the student is a type which is structure consisting of
data members: name, age, roll and class.
Declare Structure Variables:
A programmer is
allowed to declare one or more structure variables along with the structure
declaration. There
are two ways to declare structure variable:
1. By struct keyword within
main() function
2. By declaring a variable at
thes time of defining the structure.
struct student s1, s2;
or
struct
student
{
Int
rollno’
char
name[20];
}s1.s2.s3,s4;
Accessing Structure Members
Structure members are accessed using the
structure member operator (.), also called the dot operator, between the
structure name and the member name.
For
example: The Structure
variable s1 has four members; name, age, roll and class. These members can be
designated as: s1.name, s1.age, s1.roll and s1.class respectively.
s1.name=”PALVI”;
s1.age=9;
s1.roll=3;
s1.class=”3rd”
Example of Structure
#include<stdio.h>
#include<conio.h>
void main()
{
struct student
{
char name[20];
int rollno;
int marks;
};
struct student s1;
clrscr();
printf(“\nEnter the Name”);
scanf(“%s”,s1.name);
printf(“\nEnter the Rollno”);
scanf(“%d”,s1.rollno);
printf(“\nEnter the Marks”);
scanf(“%d”,s1.marks);
printf(“\nStudent Details is %s\t%d\t%d”,s1.name,s1.rollno,s1.marks);
getch();
}
Pointers and Structures
Similar to other types of pointers, we can
have a structure pointer also .that means we can also point a pointer to a
structure.
Pointer to structure means we can assign the
address of a structure to the structure type pointer variable.
To access the member of structure by the
structure pointer we can use the (->) operator.
Syntax: struct structure_name
*pointer_variable_name;
Program
#include<stdio.h>
#include<conio.h>
struct student
{
char name[20];
int rollno;
};
void main()
{
struct student stu;
struct student *p;
p=&stu;
printf(“\n Enter Student Name:”);
scanf(“%s”,p->name);
printf(“\n Enter Student Roll No:”);
scanf(“%d”,p->rollno);
printf(“\n******OUTPUT******);
printf(“\n Student Name is :%s”,(*p).name);
printf(“\n Student Rollno is
:%d”,(*p).rollno);
getch();
}
Passing Structures to Functions
The Structure variables can also be passed to
a function as arguments both by value and by a reference.
Call by Value
In this method of passing the structures to
functions, a copy of the actual arguments is passed to the function.
Program
#include<stdio.h>
#include<conio.h>
void disp(struct student s1);
struct student
{
char name[20];
int rollno;
};
void main()
{
struct student stu;
printf(“Enter the Name”);
scanf(“%s”,&stu.name);
printf(“Enter the RollNo”);
scanf(“%d”,&stu.rollno);
disp(stu);
getch();
}
void disp(struct student s1)
{
printf(“\n****output****”);
printf(“\nStudent Name is %s”,s1.name);
printf(“\nStudent Rollno is %d”,s1.rollno);
}
Call
by reference
In this method of passing the structures to
functions, the address of the actual structure variable is passed.
The address of the structure variable is
obtained with the help of address operator’&’.
Program
#include<stdio.h>
#include<conio.h>
void disp(struct student * s1);
struct student
{
char name[20];
int rollno;
};
void main()
{
clrscr();
struct student stu;
printf(“Enter the Name”);
scanf(“%s”,&stu.name);
printf(“Enter the RollNo”);
scanf(“%d”,&stu.rollno);
disp(&stu);
getch();
}
void disp(struct student *s1)
{
printf(“\n****output****”);
printf(“\nStudent Name is %s”,s1->name);
printf(“\nStudent Rollno is
%d”,s1->rollno);
}
Unions
Unions are similar to Structures. A union is
declared and used in the same ways that a structure.
Union is also a derived data type in C and
they are much like structure. The only difference is that in structures, each
variable has the separate memory allocation for each element but in union variables use the same memory location.
The
general form of union declaration is:-
Unions are defined and declared in the same
as structure. The only difference is the declaration is that the keyword union
is used instead of struct.
Syntax
union<union_name>
{
datatype member 1;
datatype member 2;
.
.
datatype member n;
};
var1, var2……,varn;
Union
·
Each
member of a union shares the same block of memory.
·
Nested
unions can be used.
·
A union
can use a structure as its member.
|
IMP |
|
Structure |
Union |
|
1.The keyword Struct is used to define a structure. |
1.The keyword union is used to define a structure. |
|
2. Structure are used to store different members at
different places in memory. |
2. Structure are used to store different members at same
memory location. |
|
3.Structure are not used to conserve memory. |
3. Structure are used to conserve memory. |
|
4. In Structure multiple
members can be can be initializing at same time |
4. In case of Union only
the first member can get initialize at a time. |
|
5.Syntax
of declare a Structure in C is as follow : struct struct_name{ type element1; type element2; . . } variable1, variable2, ...; |
5.On
other syntax of declare a Union in C is as follow: union u_name{ type element1; type element2; . . } variable1, variable2, ...; |
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