Arrays are used to store large set of data and manipulate them but the
disadvantage is that all the elements stored in an array are to be of
the same data type. If we need to use a collection of different data
type items it is not possible using an array. When we require using a
collection of different data items of different data types we can use a
structure. Structure is a method of packing data of different types. A
structure is a convenient method of handling a group of related data
items of different data types.
structure definition:
general format:
struct tag_name
{
data type member1;
data type member2;
}
Example:
struct lib_books
{
char title[20;
char author[1!;
int pages;
float price;
};
the keyword struct declares a structure to holds the details of four
fields namely title, author pages and price. These are members of the
structures. ach member may belong to different or same data type.
The tag name can be used to define ob!ects that have the tag names
structure. The structure we !ust declared is not a variable by itself but
a template for the structure.
We can declare structure variables using the tag name any where in
the program. "or e#ample the statement,
struct lib_books book1"book2"book#;
declares book$,book%,book& as variables of type struct lib'books each
declaration has four elements of the structure lib'books. The complete
structure declaration might look like this
struct lib_books
{
char title[20;
char author[1!;
int pages;
float price;
};
struct lib_books" book1" book2" book#;
structures do not occupy any memory until it is associated with the
structure variable such as book$. the template is terminated with a
semicolon. While the entire declaration is considered as a statement,
each member is declared independently for its name and type in a
separate statement inside the template. The tag name such as
lib'books can be used to declare structure variables of its data type
later in the program.
We can also combine both template declaration and variables
declaration in one statement, the declaration
struct lib_books
{
char title[20;
char author[1!;
int pages;
float price;
} book1"book2"book#;
is $alid% &he use of tag name is optional for e'ample
struct
{
}
book$, book%, book& declares book$,book%,book& as structure
variables representing & books but does not include a tag name for use
in the declaration.
A structure is usually defines before main along with macro definitions.
In such cases the structure assumes global status and all the functions
can access the structure.
Giving values to members:
As mentioned earlier the members themselves are not variables
they should be linked to structure variables in order to make
them meaningful members. The link between a member and a
variable is established using the member operator (.) Which is
known as dot operator or period operator.
For example:
(ook1%price
Is the variable representing the price of book$ and can be
treated like any other ordinary variable. We can use scanf
statement to assign values like
scanf)*+s,"book1%file-;
scanf)*+d,". book1%pages-;
*r we can assign variables to the members of book$
strcpy)book1%title",basic,-;
strcpy)book1%author",(alagurusamy,-;
book1%pages/2!0;
book1%price/20%!0;
12 3'ample program for using a structure21
4include5 stdio%h 6
$oid main)-
{
int id_no;
char name[20;
char address[20;
char combination[#;
int age;
}ne7student;
printf)*3nter the student information,-;
printf)*8o7 3nter the student id_no,-;
scanf)*+d,".ne7student%id_no-;
printf)*3nter the name of the student,-;
scanf)*+s,".ne7 student%name-;
printf)*3nter the address of the student,-;
scanf)*+s,".ne7 student%address-;
printf)*3nter the cmbination of the student,-;
scanf)*+d,".ne7 student%combination-;
printf)*3nter the age of the student,-;
scanf)*+d,".ne7 student%age-;
printf)*9tudent information:n,-;
printf)*student id_number/+d:n,"ne7student%id_no-;
printf)*student name/+s:n,"ne7student%name-;
printf)*student ;ddress/+s:n,"ne7student%address-;
printf)*students combination/
+s:n,"ne7student%combination-;
printf)*;ge of student/+d:n,"ne7student%age-;
}
Initializing structure:
+ike other data type we can initiali,e structure when we declare
them. As for initali,ation goes structure obeys the same set of
rules as arrays we initali,e the fields of a structure by the
following structure declaration with a list containing values for
weach fileds as with arrays these values must be evaluate at
compile time.
Example:
Struct student newstudent
-
$%&./,
0kapildev1
02es college13
04se13
$53
63
this initiali,es the id'no field to $%&./, the name field to
0kapildev1, the address field to 0pes college1 the field
combination to 0cse1 and the age field to $5.
Functions and structures:
We can pass structures as arguments to functions. 7nlike array
names however, which always point to the start of the array,
structure names are not pointers. As a result, when we change
structure parameter inside a function, we don)t effect its
corresponding argument.
2assing structure to elements to functions8
A structure may be passed into a function as individual member
or a separate variable.
A program e#ample to display the contents of a structure passing
the individual elements to a function is shown below.
4 include 5 stdio%h 6
$oid main)-
{
int emp_id;
char name[2!;
char department[10;
float salary;
};
static struct emp1/{12!",sampath,",operator,"<!00%00};
12 pass only emp_id and name to display function21
display)emp1%emp_id"emp1%name-;
}
12 function to display structure $ariables21
display)e_no"e_name-
int e_no"e_name;
{
printf)*+d+s,"e_no"e_name-;
in the declaration of structure type, emp'id and name have been
declared as integer and character array. When we call the
function display9: using display9emp$.emp'id,emp$.name:3
we are sending the emp'id and name to function display9;:3
it can be immediately reali,ed that to pass individual elements
would become more tedious as the number of structure elements
go on increasing a better way would be to pass the entire
structure variable at a time.
Passing entire function to functions:
In case of structures having to having numerous structure
elements passing these individual elements would be a tedious
task. In such cases we may pass whole structure to a function as
shown below8
4 include stdio%h6
{
int emp_id;
char name[2!;
char department[10;
float salary;
};
$oid main)-
{
static struct employee emp1/
{
12"
*sadanand,"
*computer,"
<!00%00
};
12sending entire employee structure21
display)emp1-;
}
12function to pass entire structure $ariable21
display)empf-
struct employee empf
{
printf)*+d+s"+s"+f,"
empf%empid"empf%name"empf%department"empf%salary-;
}
Arrays of structure:
It is possible to define a array of structures for e#ample if we are
maintaining information of all the students in the college and if
$;; students are studying in the college. We need to use an
array than single variables. We can define an array of structures
as shown in the following e#ample8
structure information
{
int id_no;
char name[20;
char address[20;
char combination[#;
int age;
}
student[100;
An array of structures can be assigned initial values !ust as any
other array can. <emember that each element is a structure that
must be assigned corresponding initial values as illustrated
below.
4include5 stdio%h 6
{
struct info
{
int id_no;
char name[20;
char address[20;
char combination[#;
int age;
}
struct info std[100;
int ="n;
printf)*3nter the number of students,-;
scanf)*+d,".n-;
printf)* 3nter =d_no"name address combination age:m,-;
for)=/0;= 5 n;=>>-
scanf)+d+s+s+s
+d,".std[=%id_no"std[=%name"std[=%address"std[=%com
bination".std[=%age-;
printf)*:n 9tudent information,-;
for )=/0;=5 n;=>>-
printf)*+d+s+s+s+d:n,"
,"std[=%id_no"std[=%name"std[=%address"std[=%combin
ation"std[=%age-;
}
Structure witin a structure:
A structure may be defined as a member of another structure. In
such structures the declaration of the embedded structure must
appear before the declarations of other structures.
struct date
{
int day;
int month;
int year;
};
struct student
{
int id_no;
char name[20;
char address[20;
char combination[#;
int age;
structure date def;
structure date doa;
}oldstudent" ne7student;
the sturucture student constains another structure date as its
one of its members.
!nion:
7nions like structure contain members whose individual data
types may differ from one another. =owever the members that
compose a union all share the same storage area within the
computers memory where as each member within a structure is
assigned its own unique storage area. Thus unions are used to
observe memory. They are useful for application involving
multiple members. Where values need not be assigned to all the
members at any one time. +ike structures union can be declared
using the keyword union as follows8
union item
{
int m;
float p;
char c;
}
code;
this declares a variable code of type union item. The union
contains three members each with a different data type. =owever
we can use only one of them at a time. This is because if only
one location is allocated for union variable irrespective of si,e.
The compiler allocates a piece of storage that is large enough to
access a union member we can use the same synta# that we use
to access structure members. That is
code%m
code%p
code%c
are all valid member variables. >uring accessing we should make
sure that we are accessing the member whose value is currently
stored.
"or e#ample a statement such as
code%m/?!@;
code%p/?!@%<0;
printf)*+d,"code%m-;
Would prodece erroneous result.
In effect a union creates a storage location that can be used by one of
its members at a time. When a different number is assigned a new
value the new value supercedes the previous members value. 7nions
may be used in all places where a structure is allowed. The notation
for accessing a union member that is nested inside a structure remains
the same as for the nested structure.
"ead #ext: C Programming - Pointers
Example:
main)-
{
$oid starline)-;
$oid message)-;
AAAAAAA
}
$oid printline
{
statements;
}
$oid $alue
{
statements;
}
