array records and pointer

1. Course: MCA
Subject: Data and File Structure
Unit-2
String, Record and Pointer

2. Definition of a Record
 A data type created/customisable by the
programmer
 consisting of a set of fields/multiple data items
 which can be of different data types

3. Records
 Arrays can only hold data items with the same type
 Records can contain different types of data
 This makes them more complex to manipulate
 Associated with databases

4. Record Example[1]
Field Type
Surname String
FirstName String
Gender Character
Address String
PostCode String
Customer Number String
A record can be considered as a two dimensional array with different data types.

5. Record Example[2]
Surname FirstName Sex Address 1 PostCode ‘phone
Tod Andy M 35 Brookside
Dr
TY7 8UK 225 3625
Boyd Mary F 27 The Grange OB7 RF1 335 2901
Bell Charles M 2 Larch Rd HT5 WA3 213 1157

6. Records[3]
In the computer’s memory, records are stored as
Record 1 * Record 2 * Record 3 * Record 4 * Record 5 * EOF
Each record is terminated by a CR, LF (indicated by *)
and EOF control codes.

7. Assigning values
BookInfo.Title = InputBox("Enter the title of the book")
BookInfo.Author = InputBox("Enter the author's name")
BookInfo.ISBN = InputBox("Enter the ISBN")
BookInfo.Price = InputBox("Enter the price")

8. Displaying record values
ListBox1.Items.Add("Title-" & BookInfo.Title)
ListBox1.Items.Add("Author-" & BookInfo.Author)
ListBox1.Items.Add("ISBN-" & BookInfo.ISBN)
ListBox1.Items.Add("Price- £" & BookInfo.Price)

9. Comparison of Arrays v. Records
 Arrays (1D & 2D)– all data must be of same type (Integer,
string,..)
 Records – fields of different types
 Arrays – simple to implement
 Records – more complex to implement

10. Arrays
An array is an indexed set of variables, such as
dancer[1], dancer[2], dancer[3],… It is like a set of boxes
that hold things.
A list is a set of items.
An array is a set of variables that each store an item.

11. Arrays and Lists[4]
You can see the difference between arrays and lists
when you delete items.

12. What is a pointer
• In a generic sense, a “pointer” is anything that tells us
where something can be found.
– Addresses in the phone book
– URLs for webpages
– Road signs

13. Java Reference
• In Java, the name of an object is a reference to that
object. Here ford is a reference to a Truck object. It
contains the memory address at which the Truck
object is stored.
 Truck ford = new Truck( );
• The syntax for using the reference is pretty simple.
Just use the “dot” notation.
 ford.start( );
 ford.drive( 23 );
 ford.turn (LEFT);

14. What is a pointer ?
• In C, a pointer variable (or just “pointer”) is similar to a
reference in Java except that
– A pointer can contain the memory address of any
variable type (Java references only refer to objects)
– A primitive (int, char, float)
– An array
– A struct or union
– Dynamically allocated memory
– Another pointer
– A function
– There’s a lot of syntax required to create and use
pointers

15. Why Pointers?
• They allow you to refer to large data structures in
a compact way
• They facilitate sharing between different parts of
programs
• They make it possible to get new memory
dynamically as your program is running
• They make it easy to represent relationships
among data items.

16. Pointer Caution
• They are a powerful low-level device.
• Undisciplined use can be confusing and thus the
source of subtle, hard-to-find bugs.
– Program crashes
– Memory leaks
– Unpredictable results

17. C Pointer Variables
 To declare a pointer variable, we must do two things
 Use the “*” (star) character to indicate that the
variable being defined is a pointer type.
 Indicate the type of variable to which the pointer
will point (the pointee). This is necessary
because C provides operations on pointers (e.g.,
*, ++, etc) whose meaning depends on the type of
the pointee.
 General declaration of a pointer
 type *nameOfPointer;

18. Pointer Declaration
The declaration
int *intPtr;
defines the variable intPtr to be a pointer to a variable of
type int. intPtr will contain the memory address of some
int variable or int array. Read this declaration as
– “intPtr is a pointer to an int”, or equivalently
– “*intPtr is an int”
Caution -- Be careful when defining multiple variables on the
same line. In this definition
int *intPtr, intPtr2;
intPtr is a pointer to an int, but intPtr2 is not!

19. Pointer Operators
 The two primary operators used with pointers are
 * (star) and & (ampersand)
 The * operator is used to define pointer variables
and to deference a pointer. “Dereferencing” a
pointer means to use the value of the pointee.
 The & operator gives the address of a variable.
 Recall the use of & in scanf( )

20. Pointer and Variable types
• The type of a pointer and its pointee must match
int a = 42;
int *ip;
double d = 6.34;
double *dp;
ip = &a; /* ok -- types match */
dp = &d; /* ok */
ip = &d; /* compiler error -- type mismatch */
dp = &a; /* compiler error */

21. More Pointer Code
• Use ampersand ( & ) to obtain the address of the pointee
• Use star ( * ) to get / change the value of the pointee
• Use %p to print the value of a pointer with printf( )
• What is the output from this code?
int a = 1, *ptr1;
/* show value and address of a ** and value of the pointer */
ptr1 = &a ;
printf("a = %d, &a = %p, ptr1 = %p, *ptr1 = %dn",
a, &a, ptr1, *ptr1) ;
/* change the value of a by dereferencing ptr1
** then print again */
*ptr1 = 35 ;
printf(“a = %d, &a = %p, ptr1 = %p, *ptr1 = %dn", a, &a, ptr1, *ptr1) ;

22. References
 An introduction to Datastructure with application by jean Trembley and sorrenson
 Data structures by schaums and series –seymour lipschutz
 http://en.wikipedia.org/wiki/Book:Data_structures
 http://www.amazon.com/Data-Structures-Algorithms
 http://www.amazon.in/Data-Structures-Algorithms-Made-Easy/dp/0615459811/
 http://www.amazon.in/Data-Structures-SIE-Seymour-Lipschutz/dp
LIST OF IMAGES
1. searchoracle.techtarget.com/definition/record
2. en.wikipedia.org/wiki/Array_list
3. An introduction to Datastructure with application by jean Trembley and sorrenson
4. en.wikipedia.org/wiki/Array_list