We have been using arrays to store similar data linearly. While arrays are
simple to understand and easy to implement in common situations, they do suffer
from some drawbacks which are listed below:
Arrays have fixed dimensions, even if we dynamically allocate the dimension
it remains constant throughout. So there is a limit to the number of elements
it can store.Operations such as insertion and deletion are pretty much difficult to
implement and increases the overhead because these operations require elements
in the array to be physically shifted.
Linked lists overcome these drawbacks and are commonly used to store linear
data.
Actually elements of linked lists (called as nodes) store two information,
data and the link (pointer) pointing to the next elements (node).
The elements (nodes) are linked sequentially with the help of link pointers.
So we can say that linked lists are collection of nodes which have data and
are linked sequentially so that all the nodes or elements are grouped together.
In programming sense, linked lists are classes whose general form is:
class node
{
public:
data-type info;
node *link;
};Here info stores the actual data while link stores the memory
address of the next node, which forms the link between the nodes.
FIG.: Graphical representation of a node
Following figure illustrates the growing of linked lists, the node which has
its link as NULL is the last element in the linked list.
FIG.: Linked lists grows like this
Let us now discuss a bit about how a linked list grows:
We have a pointer that stores the memory address of the first element
in the linked list, represented as the start pointer (of type node). It
is NULL to begin with as we don’t have any element in the list.As an element is added, the start pointer is made to point at it and since
for now the first element is the last element therefore its link is made
to be NULLAfter the addition of each element the link pointer of the previously last
element is made to point at new last element. This step continues…
In this way the number of nodes in a linked list can grow or shrink over time
as far as memory permits.
Below is the example program that illustrates linked lists. This program is
made as simple as possible and therefore it only performs the basic action (addition
of element) in the linked list.
// -- Linked Lists --
// ------------------
// Example program in C++
// to illustrate the most simple
// linked list
// NOTE: It is designed so that it
// could only add nodes to the
// list and display them.
#include<iostream.h>
// node class, this will
// represent the nodes or elements
// of the linked list
class node
{
public:
int info;
node *link;
};
// declare global objects
node *start=NULL;
// function prototypes
void add(int inf);
void display(void);
void main(void)
{
int ch;
// input elements
while(ch!=0)
{
cout<<"enter element to be added:";
cout<<"\nenter 0 to stop...\n";
cin>>ch;
if(ch!=0) add(ch);
cout<<"\n\n";
}
cout<<"elements are...\n";
display();
// below is a bit confusing
// part.
// here all the nodes that
// we have allocated are
// being freed up
node temp;
while(start!=NULL)
{
// store the next node
// to the one being deleted
temp=*start;
// delete the node
delete start;
// retrieve the next node
// to be deleted
start=temp.link;
}
}
void add(int inf)
{
node *temp1;
node *temp2;
// if the element to be added
// is the first element
if(start==NULL)
{
// allocate a new node
temp1=new node;
temp1->info=inf;
temp1->link=NULL;
// make start point at it
start=temp1;
}
// if not
else
{
temp1=start;
// find out the last element
while(temp1->link!=NULL)
temp1=temp1->link;
// allocate new node
temp2=new node;
temp2->info=inf;
temp2->link=NULL;
// make the last element
// of the list to point
// at the newly created node
temp1->link=temp2;
}
}
void display(void)
{
node *temp;
temp=start;
// traverse or process
// through each element
// and keep printing
// the information
while(temp!=NULL)
{
cout<<temp->info<<endl;
temp=temp->link;
}
}Good-Bye!
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