1. S. Kiran, PGT (CS) KV, Malleswaram
STRUCTURES

2. Structure is a collection of logically related data.
S. Kiran, PGT (CS) KV, Malleswaram
What is a structure ?
Structure is a collection of logically related data.
It is also a collection of dissimilar datatype.

3. Why do we need a structure ?
S. Kiran, PGT (CS) KV, Malleswaram
Why do we need a structure ?
For instance, if we want to store the information of 50 employees. Such as
employee number,
name,
age
and basic.

4. Using arrays, the declaration would be as follows: int empno[50];
S. Kiran, PGT (CS) KV, Malleswaram
Using arrays, the declaration would be as follows:
int empno[50];
char name[50][20];
int age[50];
float basic[50]
And the memory allocation would be as follows

5. empno Name age 0 …………………. . . . . . .. . .………. ………………….49 0,0 49,0
S. Kiran, PGT (CS) KV, Malleswaram
empno Name age
0 ………………… ………. ………………….49
0,0
49,0
0 ………………… ………. ………………….49

6. Drawbacks of using array
S. Kiran, PGT (CS) KV, Malleswaram
Drawbacks of using array
In the declaration made above if we want to search for a particular employee detail say for e.g. emp who is stored in index no. 30.
it has to make 30 searches to get empno, 30 searches to get name, 30 searches to get age and 30 searches to find basic.

7. S. Kiran, PGT (CS) KV, Malleswaram
So altogether to fetch one employee detail the system has to make i.e. 120 searches. Which doesn’t make the program efficient and makes the process of data retrieval and access very slow.
This drawback is over come by using the user defined datatype - STRUCTURES

8. STRUCTURE DECLARATION
S. Kiran, PGT (CS) KV, Malleswaram
STRUCTURE DECLARATION
Syntax :
struct structure tag / name {
datatype variablename; };

9. S. Kiran, PGT (CS) KV, Malleswaram
Example :
Structure name
struct student { int stdno; char name[20]; int age; float total; char grade; };
Structure elements
Remember structure declaration ends with a ;

10. S. Kiran, PGT (CS) KV, Malleswaram
Memory allocation
No memory is allocated at the time of structure declaration.
Memory is allocated only when a structure variable is declared.

11. Struct variable declaration
S. Kiran, PGT (CS) KV, Malleswaram
Struct variable declaration
For the structure declaration made
abovethe variable would be defined as follows :
Syntax:
structname variable ;
For eg:
student s ;
Structure variable
Structure name

12. Memory representation
S. Kiran, PGT (CS) KV, Malleswaram
Memory representation
For a single structure variable memory is allocated as follows :
grade
total
stdno
age
name

13. Referencing structure elements
S. Kiran, PGT (CS) KV, Malleswaram
Referencing structure elements
The elements in a structure are referenced using dot operator.
Eg.,
student s;
s.stdno;
s.name;

14. S. Kiran, PGT (CS) KV, Malleswaram
Structure as array
struct emp { int empno; char name[20]; float basic: } e[10]; Here an array to store 10 employee details is created.

15. MEMORY ALLOCATION FOR STRUCTURE
S. Kiran, PGT (CS) KV, Malleswaram
MEMORY ALLOCATION FOR STRUCTURE
EMPNO
Name
basic
0,0 .
9,0

16. struct emp cin>>e[i].empno; { cout<<“Enter Emp. Name”;
S. Kiran, PGT (CS) KV, Malleswaram
Program:
struct emp cin>>e[i].empno;
{ cout<<“Enter Emp. Name”;
int empno; cin>>e[i].name;
char ename[20]; cout<<“Enter Basic “;
float basic; cin>>e[i].basic;
}e[10]; }
void main() getch();
{ }
clrscr();
cout<<“Enter emp details” ;
for(int i=0; i<10; i++) {
cout<<“Employee No”;

17. S. Kiran, PGT (CS) KV, Malleswaram
recapitulation

18. What is the difference between an array and structure?
S. Kiran, PGT (CS) KV, Malleswaram
What is the difference between an array and structure?
What are the drawbacks of using an array?
When is memory allocated for structure datatypes?
How do we refer the elements of the structure?