Structures allow grouping of related data types together under one name. A structure defines members of different data types. Structure variables can be declared to access members using dot operator. Arrays of structures can be defined to represent multiple records. Structures can be nested by defining a structure as a member of another structure. Unions are similar to structures but share same memory space for members rather than each occupying own space like in structures.

1. Structure and Union
Topics
 Introduction
 Structure Definition
 Giving values to Members
 Structure Initialization
 Array of Structures
 Arrays within Structure

2. Introduction
 Arrays can be used to represent a group of
data items that belong to the same type.
However, if we want to represent a collection
of data items of different types using a single
name then we cannot use an array.
 C supports a user defined data type
structure for packing data of different types.
A structure is a convenient tool for handling
a group of logically related data items.

3. Structure Definition
 The general format of structure is:
struct tag_name
{
data_type member1;
data_type member2;
-----------
-----------
};
 Ex: struct student
{
char name[20];
int roll;
float gpa;
};

4. Continue…
 We can declare structure variables using the tag
name anywhere in the program. For example:
struct student s1,s2,s3;
 Each of the variable has three members and the
members are not variable.
 The declaration can be:
struct student
{
char name[20];
int roll;
float gpa;
}s1,s2,s3;

5. Giving values To members
 The link between a member and a variable is
established using the member operator (.).
 For example: s1.name is the variable representing
the name of s1 and can be treated like any other
ordinary variable.
 We can assign values to the members of s1:
strcpy(s1.name, “Rahul”);
s1.roll=1;
s1.gpa=3.79;
 We can use scanf to give values through the
keyboard.
scanf(“%s”,s1.name);
scanf(“%d”,&s1.roll);

6. Structure Initialization
 Like any other data type, a structure variable can
be initialized. A structure must be declared as
static if it is to be initialized inside a function.
 Ex:
main()
{
static struct
{
int x;
float y;
}str={101,350.789};
---------
}

7. Continue..
 Another method is to initialize a structure variable
outside the function:
struct st
{
int x;
float y;
}s={50,101.56};
main()
{
static struct st s1={200,340.50};
------------
}

8. Array of Structure
 We use structures to describe the format of
a number of related variables. We may
declare an array of structures, each element
of the array representing a structure variable
 For example:
struct student st[100]; defines an array
called st that consists of 100 elements.
Each element is defined to be of the type
struct student.

9. Structures within Structures
 Structure within a structure means nesting of structures.
 Ex:
struct st
{
char name[20];
char dept[20];
struct
{
int roll;
float gpa;
}info;
}student;
 We can use the members like student.info.roll,
student.info.gpa, student.name

10. Continue…
 We can also use tag names to define inner
structures. Example-
struct info
{
int roll;
float gpa;
};
struct st
{
char name[20];
struct info str;
};
struct st student[20];

11. Union
 Unions are the same syntax as the structure
However, there is major distinction between
them in terms of storage.
Structure Union
Every member of the
structure occupy the
memory space
The space of the largest
member will occupy for
the union
There is no limitation for
using the member
Only one member can
handle at a time