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Monday, July 23, 2007

Introduction to Linked Lists III

In the article Introduction to Linked Lists, we introduced the concept of linked list, the example program was programmed to be able to add and display the elements in the linked list. In reality only addition of elements to the linked list is not enough to take the most out of linked list; we should be able to do other operations such as insertion, deletion of elements etc.

This article would teach you to do such operation (insertion, addition, deletion etc).

The program itself is quite big and has enough comments so I won’t discuss anything here; rather I leave it up to you to understand all the operations yourself!

  // -- Linked Lists --
  // ------------------
  // Example program to illustrate
  // addition, insertion, deletion
  // and display of nodes in the 
  // linked list

  #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 insert(int, int);
  void add(int);
  void display(void);
  void del(int);
  void free();

  void main(void)
  {
   int ch,pos,num;

   while(ch!=5)
   {
    cout<<"1> Add";
    cout<<"\n2> Insert";
    cout<<"\n3> Delete";
    cout<<"\n4> Display";
    cout<<"\n5> Quit\n";

    cin>>ch;

    switch(ch)
    {
     case 1:
      cout<<"enter element:";
      cin>>num;
 
      add(num);
      break;

     case 2:
      cout<<"enter pos:";
      cin>>pos;
      cout<<"enter element:";
      cin>>num;
      insert(pos,num);
      break;

     case 3:
      cout<<"enter element to be deleted:";
      cin>>num;
      del(num);
      break;

     case 4:
      display();
      break;
    }
   }

   // free-up the allocated
   // memory
   free();
  }

  // --FUNCTION--
  // this function takes two
  // arguments, 'loc' is the 
  // number of elements after
  // which the new element having
  // value 'inf' has to be inserted
  void insert(int loc,int inf)
  {
   node *temp;
   node *temp_new;
   int i;

   // if invalid, return
if(loc<=0) return; temp=start; // skip to the desired // location where the node // is to be added for(i=1;i<loc;i++) { temp=temp->link; if(temp==NULL) { cout<<"NOT POSSIBLE!"; return; }
} // allocate new node temp_new=new node; temp_new->info=inf; // make it point to the // respective node temp_new->link=temp->link; // make the prev. node where // the new node is added, to // point at the new node temp->link=temp_new; }
  // --FUNCTION--
  // display all the data
  // in the linked list
  void display(void)
  {
   node *temp;
   temp=start;

   // traverse or process
   // through each element
   // and keep printing 
   // the information
   cout<<"\nelements are...\n";
   while(temp!=NULL)
   {
    cout<<temp->info<<endl;
    temp=temp->link;
   }
  }

  // --FUNCTION--
  // adds node to the end
  // of the linked list
  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;
   }
  }

  // --FUNCTION--
  // takes the argument of the
  // 'info' part of the node 
  // to be deleted
  void del(int inf)
  {
   node *temp, *old;

   temp=start;

   // while list not empty
   while(temp!=NULL)
   {
    // if match is found
    if(temp->info==inf)
    {
     // if it is the
     // first node
     if(temp==start)
       start=temp->link;

     else
       old->link=temp->link;

     delete temp;
     return;
    }
    else
    {
     // traverse through
     // each node
     old=temp;
     temp=temp->link;
    }
   }
  }  

  // --FUNCTION--
  // free up the allocated memory
  // used by the nodes of the
  // linked list
  void free()
  {
   // 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;
   }
  }

Good-Bye!

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