C++ program for linked lists

  Linked lists 

A linked list is a linear data structure where each element is a separate object.

• Each node of a list is comprising of two items - the data and a reference to the next node. The last node has a reference to null. 
• The entry point into a linked list is called the head of the list. It should be noted that head is not a separate node, but the reference to the first node. If the list is empty then the head is a null reference.
• A linked list is a dynamic data structure. The number of nodes in a list is not fixed and can grow and shrink on demand. 
• One disadvantage of a linked list against an array is that it does not allow direct access to the individual elements. If you want to access a particular item then you have to start at the head and follow the references until you get to that item.

Program:

#include<iostream>

using namespace std;

struct node{

int info ;

node *next ;

}*t;

node *head=NULL;

node *tail=NULL;

void add(int n)

{node *tmp=new node;

tmp->info=n;

tmp->next=NULL;

if(head ==NULL)

{head=tmp;

tail=tmp;

}

else {

tail->next=tmp;//tail changes its previous value to tmp

tail=tail->next;}

}

void beg(int n)

{node *tmp=new node;

tmp->info=n;

tmp->next=head;//Assigns next pointer of head to tmp

head=tmp;//assigns address of tmp to head

}

void end(int n) //insertion at end

{node *tmp=new node;

tmp->info=n;

tail->next=tmp;

tail=tmp;

}

void pos(node *a,int n) // insertion after a position

{node *tmp=new node;

tmp->info=n;

tmp->next=a->next;

a->next=tmp;

}

void display() //Display function

{ node *f=head;

    while(f!=NULL)

{cout<<f->info<<"->";

f=f->next;}

cout<<"!!!";

}

void del() // Delete function

{

node *tmp=new node;

tmp=head;

head=head->next;//head becomes the next node

delete tmp;

}

main()

{int val,p,ch,val1;

char c;

node *t;

do{cout<<"Enter the info to create new node :";

cin>>val;

add(val);

cout<<"Want to add more : ";

cin>>c;

}while(c=='y'||c=='Y');

t=head;

cout<<"Enter your choice \n1.Beg \n2.After a node \n3.end \n4.Delete \nChoice:" ;

cin>>ch;

switch(ch)

{case 1:cout<<"Enter value you want to insert";

cin>>val1;

    beg(val1);

break;

case 2:cout<<"Enter value you want to insert";

cin>>val1;

cout<<"Enter position you want to insert";

cin>>p;

for(int i=1;i<p;i++)

{

t=t->next;

}

    pos(t,val1);

break;

case 3:cout<<"Enter value you want to insert";

cin>>val1;

end(val1);

break;

case 4:del();}

cout<<"Display ";

display();

}
Output of the program: