A very basic as well as deep introduction about structures and unions. Engineering year 1 Subject: Computer programing and utilization

1. •STRUCTURE
•UNIONS

2. 1. INTRODUCTION
 C’ Supports a constructed data type known
as STRUCTURE, Which is a method of
packing data of different types.
WHAT IS STRUCTURE ?
 A Structure is a convenient tool for handling
a group of logically related data items.
 i.e. It can be used to represent a set of
attributes, such as : student_name , roll_no

3. A structure defination creates a
formet that may be used to declare
structure variables.
i.e. Consider a book database
consisting of a book name, Author,
Number of pages and price.
We can define a structure to hold this
information as follows:

4. Struct tag_name
{
data_type member1;
data_type member2;
… …
……… …..
};

5. 1. The template terminated with a semicolon
2. While the entire declarationn considered as a
satement, each member is declared
indepandently for its name and type in a
separate statement inside the teplate.
3. The tag name such as book_bank can be
used to declare structure variables of its
type,letter in the program.

6. Struct book_bank
{
Char title[20];
Char author[15];
Int pages;
Float price;
};

7.  The keyword struct declares a structure to
hold the details of four fields, namely
title,author,pages and price.
 These fields are called structure elements or
members and each member belong to
different type of data.
 Book_bank is the name of the structure and
also called ‘STRUCTURE TAG’.

8. title
author
pages
price
Array of 15
characters
integer
float
Array of 20 characters

9.  The link between a member and variable is
established using the member operator ‘.’
which is also known as ‘dot operator’ or
‘period operator’.
 i.e.
book1.price
 Is the variable represnting the price of book1
and can be treated like any other ordinary
variable.

10.  Here is how we would assign values to the
members of book1:
strcpy(book1.title, “COMPUTER”);
strcpy(book1.author, “XYZ”);
book1.pages=250;
book1.price=29.99;
 We can also use scanf to give the values
through keyboard.

11.  A Structure must be declared as static if it is
to be initialized inside a function.
 main()
{
static struct
{
int weight;
float height;
}
student = (60,180.75);
…..
}

12.  If there are fewer initialization than that of
member variables in the structure. The
remaining member variables are initialized to
zero.
 i.e. if we don’t know the number of pages in
book:
struct book b1={“let us
C”,”kanetkar”,0,150.50};

13.  We use structure todescribe the format of a
number related variables.
 In such cases, we may declare array of
structures,each element of an array represent
a structure variable
 i.e. struct class student[100]
 This defines an array called student , that
consists of 100 element.

14.  Each element is defined to be of the type
struct class.
 An array of structure is stored inside the
memory in the same way as a multi-
dimensional array.

15.  C permits the use of array as a structure
members.
 We can use single or multi-dimensional array
of type int or float.
 i.e. Struct marks
{
int number;
float subject[3];
} student[2];

16.  The main philosophy of c language is the use
of functions. C supports the passing of
structure values as arguments to function.
 There are 3 methods by which the values of a
structure can be transfferd from one function
to another:
1. To pass each member of the structure as an
argument of function call.

17. 2. Passing of a copy of the entire structure to
the called function
3. Pointers to pass the structure as an
argument.
 General formet of sending a copy of a
structure to thr called function:
data_type function name(st_name)
srtuct_type st_name;
{
…
return(expression);
}

18.  Unions are a concept borrowed from
structures and therefore follow the same
syntax as structures.
 Major diffferance in terms of Storage:
In structures each member has its
own storage location
In unions all members use the same
location

19.  Union may contain many members of
different type but can handle only one
member at a time.
 It can be declared using keyword union as
follows:
 union item
{
int m;
float x;
char c;
} code;

20.  Union union_name
{
data_type member1;
data_type mrmber2;
… … .. …..
} var1, var2, .. ;

21. Union book;
{
char title[15];
char *author;
int pages;
float price;
} b1, b2, b3;

22.  A union variable can be assigned to another
union variable.
 Address of the union variable is obtained
using the address of ‘&’ operator.
 It is to pass a union to function and a
function can return a union.
 We can use pointer to unions and within
unions.

23.  All members share the same storage area in
computers memory.