1. CSEB324 Data Structures & Algorithms
Chapter 2
Pointer & Linked List
CSEB324 Data Structures & Algorithms

2. Introduction
If we have a set of data, we can keep it in an array. But the problem with array is, the size is fixed
Overflow
Size can’t be extended
Wasted if unused
To overcome this – we use linked list.
To understand linked list, we must first understand the fundamentals – the pointer.

3. Pointer ? Variable concept Pointer ? Linked List?
Declaring a variable
Memory allocation
Pointer ?
A variable which give location of other variable.
Linked List?
Put a pointer in a structure, giving the next location of the next structure.
Static variable vs. Dynamic variable
Static variable – declared and named in program
Dynamic – created during program execution.

4. Understanding Pointers
Declare a pointer
int *aPtr;
int *aPtr = null;
Assigning a pointer
aPtr = &aVar;
Read the pointer value
printf(“%d “, *aPtr);

5. Exercise Declare an integer variable a and b
Declare pointer variables aPtr and bPtr
Assign a to has a value of 100, and b to has a value of 200
Assign aPtr to points to a
Assign bPtr to points to aPtr
By using bPtr, change value of a to be the same as b.

6. Linked List
a pointer in a structure, giving the next location of the next structure.
123 A C

7. Linked List - Declaration
Temp
Item Next
Llist
NULL
Linked List consist of structure
Llist – is a pointer, pointing to a linked list structure
Next is a pointer in the linked list structure

8. Structure Declaration
typedef char item; typedef struct node{ item data; struct node *next; } Node;

9. Declaring the linked list
Item Next
Llist
NULL
To declare a linked list
Node *Llist; //Llist –pointer pointing to a node type

10. Linked List Operation Create a Nod Verify for an empty list
Traversal along the linked nodes
Insert new nodes
Delete a node

11. Creating New Node
Node *newnode (item c) { Node *n; n = (Node *) malloc (sizeof (Node)); if ( n != NULL) { n-> data = c; n->next = NULL; } return n;

12. Insert New Node at the begining
Item Next
Temp
NULL
Llist X

13. Inserting node in the middle
Item Next
Temp
NULL
Llist
CurrPtr
Item Next
Temp
Llist
NULL
CurrPtr

14. Insert New Node - implementation
void InsertNode( Node *Llist, Node *temp, Node *CurrPtr){ { if (CurrPtr ==NULL) { temp->next = Llist; Llist = temp; } else { temp->next = CurrPtr->next; CurrPtr –>next = temp;

15. Traverse The List
Item Next
Llist
NULL
Item Next
Llist
NULL
Temp
void Traversal ( Node *Llist) { Node *Temp; Temp = Llist; while ( Temp != NULL) { printf (“data = %c", Temp->data); Temp = Temp-> next; }

16. Deleting first node Temp Item Next NULL Llist Temp X Item Next NULL

17. Deleting middle or last node
Temp
Item Next
Llist
NULL
CurrPtr
Temp
Item Next
Llist
NULL
CurrPtr

18. Deleting Node - implementation
void DeleteNode( Node *Llist, Node *CurrPtr) { Node *temp; if (CurrPtr ==NULL) { temp = Llist; Llist = temp->next; } else { temp = CurrPtr->next; CurrPtr –>next = temp->next; free(temp)

19. Type of Linked List
Simple one-way linked list x1 x4 x2 x3 L

20. Type of Linked List Circular Linked List
Formed by having the link in the l ast node of a one way linked list point back to the first node. x1 x4 x2 x3 L

21. Type of Linked List Two Way Linked List
Formed from nodes that have pointers to both their left and right neighbours in the list L x1 x2 x3

22. Type of Linked List Linked List with Header Node
Header points to the first node
As a marker / stopping place
Ease the deletion process of a node
Header Node x1 x4 L x2 x3 L

23. Exercise 2 Indicate whether the statement is TRUE or FALSE
typedef struct bmi {
int age; float weight;
struct bmi *next;
} BMI;
BMI *mybmi;
Indicate whether the statement is TRUE or FALSE
The following code segment is to traverse and display all data from the linked list.
while (mybmi != NULL)
printf(“%d %.2f”, mybmi->age, mybmi->weight);

24. Exercise 2 (cont..) Indicate whether the statement is TRUE or FALSE
typedef struct bmi {
int age; float weight;
struct bmi *next;
} BMI;
BMI *mybmi;
Indicate whether the statement is TRUE or FALSE
Assume q has been declared as a pointer of type BMI, then the statement to create a dynamic storage of type BMI is as follows:
q = (BMI*) malloc (sizeof(BMI));

25. Exercise 3 Write code segment to delete a node with value 15.00.
Given,
ListGame *temp;
temp = (ListGame*) malloc (sizeof(ListGame));
temp -> data = 12.0 ; temp->link = NULL;
Write a code segment to insert this node after the first node in above linked list.

26. Exercise 4
Given,
struct Student
{ char name [20];
float cgpa;
Student *next; };
Refer to the diagram, write code segment to delete the node Siew Chee.

27. Linked List Using Array
Older and widely used computer language (COBOL, Fortran, BASIC) do not provide facilities for dynamic storage allocation (pointers)
Workspace (several arrays hold different part of a logical record) is used for programming languages which do not support records.

28. Linked List Using Array
Implementation of linked list using array is preferred if:
Number of entries is known in advance
Few insertions or deletions
Data are sometimes best treated as a linked list and other times as a contiguous

29. Linked List Using Array
typedef char ListEntry; typedef int ListIndex; typedef struct listnode{ ListEntry entry; ListIndex next; } ListNode; typedef int Position; typedef struct list{ ListIndex head; int count; }List; ListIndex avail,lastused; ListNode workspace[10]

30. Array Linked List – New Node
ListIndex NewNode (void) { ListIndex newindex = -1; if(avail != -1) { newindex = avail; avail = workspace[avail].next; workspace[newindex].next = 0; } else if (lastused < MAXLIST - 1) { newindex = ++lastused; else printf (“ Error Overflow : workspace for linked list is full”); return newindex;

31. Array Linked List - Insert
void InsertList ( Position p, ListEntry x, List *list) { ListIndex newindex, previous; if ( p <0 || p > list->count) printf(“ Error inserting into a nonexistent position”); else { newindex = NewNode(); workspace[newindex].entry = x; if (p == 0) { workspace[newindex].next = list->head; list->head = newindex; } else { SetPosition(p-1, &previous, list); workspace[newindex].next=workspace[previous].next; workspace[previous].next = newindex; list->count ++;

32. Array Linked List - Dispose
void DisposeNode (ListIndex oldindex, List *list) { ListIndex previous; if( oldindex == -1) printf(“Error : Disposing a nonexistent node”); else { if ( oldindex == list-> head) list->head = workspace[oldindex].next; SetPosition(CurrentPosition(oldindex,list)– 1, &previous, list); workspace[previous].next=workspace[oldindex].next; } workspace[oldindex].next = avail; avail = oldindex;

33. Array Linked List - Traverse
void TraverseList (List *list) {
ListIndex current;
for (current= list->head ; current != -1; workspace[current].next)
printf(”data of workspace[%d].entry = %c”, current,
workspace[current].entry); }

34. Class Exercise
Write a complete program to create, insert and delete a linked list. Each list will consist of ID (an integer) and Grade (a character)
Guides
Declare linked list structure
Writes all the ADT funtions (newNode, InsertNode, DeleteNode, TraverseNode)
In main program:
Create new node
Traverse the list
Create another node
Insert into the existing list
Traverse list
Delete the last node
Insert new node