CHAPTER 10
“STRUCTURES AND UNIONS”
INTRODUCTION TO STRUCTURE
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. 2
DEFINING STRUCTURE
The general form for defining structure:
struct tag_name
{
data type member1;
data type member2;
…
…
};
Create a structure Book to store book details
The keyword struct declares a structure to holds the details of
four fields namely title, author, pages and price.
These are members or elements of the structures. Each
member may belong to different or same data type.
The tag name can be used to define objects that have the tag
names structure.
3
The structure we just declared is not a variable by itself but a
template for the structure.
DEFINING STRUCTURE
Example:
struct lib_books
{
char title[20];
char author[15];
int pages;
float price;
};
4
DECLARING STRUCTURE VARIABLE
To access structure item, we require to create
structure variable (object).
A structure variable declaration is similar to
the declaration of variables of any other data
types.
It includes the following elements:
1. The keyword struct.
2. The structure tag name.
3. List of variable names separated by names.
4. A terminating semicolon.
Syntax:- 5
struct structure_name variable_name;
DECLARING STRUCTURE VARIABLE
We can declare structure variables using the
tag name any where in the program.
For example the statement,
struct lib_books book1,book2,book3;
declares book1,book2,book3 as variables of type
struct lib_books each declaration has four
elements of the structure lib_books.
Structures do not occupy any memory until it is
associated with the structure variable such as book1.
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DECLARING STRUCTURE VARIABLE
We can also combine both template declaration
and variables declaration in one
Statement, the declaration
struct lib_books
{
char title[20];
char author[15];
int pages;
float price;
} book1,book2,book3;
is valid. 7
DECLARING STRUCTURE VARIABLE
The use of tag name is optional for example
struct
{
…
…
…
} book1, book2, book3 ;
declares book1,book2,book3 as structure variables
representing 3 books but does not include a tag name
for use in the declaration.
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ACCESSING STRUCTURE MEMBERS
The link between a member and a variable is
established using the member selection operator ‘.’
which is known as dot operator or period
operator.
For example:
Book1.price
is the variable representing the price of
book1 and can be treated like any other
ordinary variable. 9
ACCESSING STRUCTURE MEMBERS
We can use scanf statement to assign values
like
scanf(“%s”,book1.title);
scanf(“%d”,&book1.pages);
or we can assign variables to the members of
book1
strcpy(book1.title,”basic”);
strcpy(book1.author,”Balagurusamy”);
book1.pages=250;
book1.price=285.0; 10
Write a C program that demonstrates the use of
structure.
#include<stdio.h> scanf("%s",s2.name);
#include<conio.h> printf("Enter the roll number of
struct student student2:");
{ scanf("%d",&s2.num);
char name[20]; printf("Enter the marks of student2:");
int num; scanf("%f",&s2.marks);
float marks; printf("Detail of Students\n");
};
int main() printf("______________________________
{ ___\n");
struct student s1,s2; printf("%s\n",s1.name);
printf("Enter the name of student1:"); printf("%d\n",s1.num);
scanf("%s",s1.name); printf("%f\n",s1.marks);
printf("Enter the roll number of
student1:"); printf("______________________________
scanf("%d",&s1.num); ____\n");
printf("Enter the marks of student1:"); printf("%s\n",s2.name);
scanf("%f",&s1.marks); printf("%d\n",s2.num);
printf("Enter the name of student2:"); printf("%f\n",s2.marks);
return 0; 11
}
Write a program to create structure name student. Enter the
student’s name, Roll No, and marks of five subjects. Find out the
percentage and also define the grade of the student.
#include<stdio.h> if(s1.per>=90 && s1.per<=100)
#include<string.h> strcpy(s1.grade,"A+");
else if(s1.per>79 && s1.per<90)
struct student strcpy(s1.grade,"A");
{ else if(s1.per>69 && s1.per<80)
char name[50]; strcpy(s1.grade,"B+");
char rollno[50]; else if(s1.per>59 && s1.per<70)
int m1,m2,m3,m4,m5; strcpy(s1.grade,"B");
float per; else if(s1.per>49 && s1.per<60)
char grade[3]; strcpy(s1.grade,"C+");
}; else if(s1.per>39 && s1.per<50)
strcpy(s1.grade,"C");
int main() else
{ strcpy(s1.grade,"F");
struct student s1;
printf("Enter the name, rollno & marks of five printf("\nName=%s\nRoll
subjects"); No=%s\nPercentage=%f\nGrade=
scanf("%s%s%d%d%d%d%d",s1.name,s1.rollno,& %s",s1.name,s1.rollno,s1.per,s1.gra
s1.m1,&s1.m2,&s1.m3,&s1.m4,&s1.m5); de);
s1.per = printf("\nSize of struct is
(float)(s1.m1+s1.m2+s1.m3+s1.m4+s1.m5)/5; %d",sizeof(s1)); 12
return 0;
}
COMPARING AND COPYING STRUCTURE VARIABLES
STRUCTURE INITIALIZATION
Example,
struct student
{
int weight;
float height;
} s3 = {70,181.57};
struct student s1={61,161.51};
struct student s2={55,150.25};
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ARRAYS OF STRUCTURES
We may declare an array of structures, each
element of the array representing a structure
variable.
For example,
struct lib_books book[100];
This declares the book as an array of 100
elements book[0],book[1],book[2],…, and
book[99].
We can access structure members using array
index like,
book[0].price=100; book[1].price = 150;
15
Write a C program that demonstrates the use of arrays
of structure.
#include<stdio.h> for(i=0; i<5; i++)
#include<conio.h> {
struct student printf("Enter the name, number
{ and marks of student %d:",i);
char name[20]; scanf("%s%d%f",s[i].name,
int num; &s[i].num,&s[i].marks);
float marks; }
}; printf("Detail of Students\n");
int main() for(i=0;i<5;i++)
{ {
struct student s[5]; printf(“\nName:%s \nNumber:%d
int i; \nMarks%f\n",s[i].name,
s[i].num,s[i].marks);
} 16
return 0;
}
UNIONS
Unions follows the same syntax as structures
The major distinction between the two is in terms of
storage
In structures, each member has its own storage
location whereas all members of a union use the same
storage location.
It implies that although a union may contain many
members of different types, it can handle only
member at a time.
The size of a union is equal to the size of it's largest
data member.
Fig. 10.7 Sharing of a storage locating by union members
Thank You
