Introduction to C Programming CE003121

1
Introduction to C ProgrammingCE00312-1

• Lecture 19
• Linear Linked Lists

2
Insertion into an ordered array
3 5 8 12 23 34 44 50 56 76

A
0 1 2 3 4 5 6 7 8
9 10 11

• Suppose we wanted to insert the value, 7.
• To keep the integers in ascending order, we cant
  just store this 7 in element A10.
• We would have to shift all elements from A2 to
  A9 one location to the right, and then store
  the 7 in A2.

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Insertion into an ordered array

• This is very cumbersome for a large array and if
  many insertions are required.
• Sooner or later we would run out of space in the
  array
• But, if we make the array very large, then most
  of the time most of the space is wasted!
• Deletion of values from the array causes similar
  problems.
• So as not to leave gaps, many values would have
  to be shifted left for each deletion.
• We should not use arrays if we need to make
  insertions and deletions.

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Linear Linked List
list
3
5
8
12 -

• Each node may be stored anywhere in memory
• and can only be reached by a pointer.
• The pointer variable, list, points to the first
  node
• and each node points to the next node.
• The last node has a NULL pointer (-).

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Insertion into a ordered Linear Linked List
list
3
5
8
12 -
7
new

• To insert an item, e.g. 7, between two nodes
  requires
• creating a new node and
• linking it with the other two nodes using just
  two pointers.

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Node Structure
value next

• struct node
• int value
• struct node next
• typedef struct node Listpointer
• // Listpointer is new type

7
Here is a header file - LLL.h containing
structure type definitions and function
prototypes for linked lists include
"stdio.h // NULL defined here include
"stdlib.h" // for malloc function struct node
int value struct node next typedef
struct node Listpointer // new type void
print_list(Listpointer) // prototypes void
print_reverse(Listpointer) Listpointer
insert(int, Listpointer) int add_items(Listpoint
er) Listpointer delete(int, Listpointer) int
search(int, Listpointer)
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print_list function

• When ptr is NULL then it is not pointing to
  anything,
• ie there is no list, or in the loop, no more
  nodes in the list.
• include "LLL.h // structure,type,prototypes
• void print_list(Listpointer ptr)
• while (ptr ! NULL)
• printf("d\n", ptr -gt value)//print value
• ptr ptr -gt next // point to next

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ptr
3
5
8
12 -
value next
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add_items function

• include "LLL.h
• int add_items(Listpointer ptr)
• int sum 0
• while (ptr ! NULL)
• sum sum ptr -gt value
• ptr ptr -gt next
• return sum

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include "LLL.h" int search(int item,
Listpointer ptr) while (ptr ! NULL) //
not end of list if (ptr -gt value
item) return 1 // true else
ptr ptr -gt next // end while return
0 // false // end search