Simple linked list in C

Question

I am about to create a linked that can insert and display until now   struct Node       int x      Node  next       This is my initialisation function which only will be called for the first Node   void initNode struct Node  head  int n       head- gt x   n      head- gt next   NULL      To add the Node  and I think the reason why my linked list isn t working correct is in this function   void addNode struct Node  head  int n       struct Node  NewNode   new Node      NewNode- gt  x   n      NewNode - gt  next   head      head   NewNode      My main function   int  tmain int argc   TCHAR  argv          struct Node  head   new Node       initNode head  5       addNode head  10       addNode head  20       return 0      Let me run the program as I think it works  First I initialise the head Node as a Node like this   head     5    NULL     Then I add a new node with n   10 and pass head as my argument   NewNode     x   next   where next points at head  And then I change the place where head is pointing to NewNode  since NewNode is the first Node in LinkedList now   Why isn t this working  I would appreciate any hints that could make me move in the right direction  I think LinkedList is a bit hard to understand   When I m printing this  it only returns 5

User · Answer

head is defined inside the main as follows   struct Node  head   new Node    But you are changing the head in addNode   and initNode   functions only  The changes are not reflected back on the main   Make the declaration of the head as global and do not pass it to functions   The functions should be as follows   void initNode int n       head- gt x   n      head- gt next   NULL     void addNode int n       struct Node  NewNode   new Node      NewNode- gt  x   n      NewNode- gt next   head      head   NewNode

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Both functions are wrong  First of all function initNode has a confusing name  It should be named as for example initList and should not do the task of addNode  That is  it should not add a value to the list   In fact  there is not any sense in function initNode  because the initialization of the list can be done when the head is defined   Node  head   nullptr    or  Node  head   NULL    So you can exclude function initNode from your design of the list   Also in your code there is no need to specify the elaborated type name for the structure Node that is to specify keyword struct before name Node   Function addNode shall change the original value of head  In your function realization you change only the copy of head passed as argument to the function   The function could look as   void addNode Node   head  int n        Node  NewNode   new Node  n   head        head   NewNode      Or if your compiler does not support the new syntax of initialization then you could write  void addNode Node   head  int n        Node  NewNode   new Node      NewNode- gt x   n      NewNode- gt next    head       head   NewNode      Or instead of using a pointer to pointer you could use a reference to pointer to Node  For example   void addNode Node    amp head  int n        Node  NewNode   new Node  n  head       head   NewNode      Or you could return an updated head from the function   Node   addNode Node  head  int n        Node  NewNode   new Node  n  head       head   NewNode      return head      And in main write   head   addNode head  5

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Use    include lt iostream gt   using namespace std   struct Node       int num      Node  next      Node  head   NULL  Node  tail   NULL   void AddnodeAtbeggining        Node  temp   new Node      cout  lt  lt   Enter the item       cin  gt  gt  temp- gt num      temp- gt next   NULL      if  head    NULL                head   temp          tail   temp            else               temp- gt next   head          head   temp           void addnodeAtend         Node  temp   new Node      cout  lt  lt   Enter the item       cin  gt  gt  temp- gt num      temp- gt next   NULL      if  head    NULL           head   temp          tail   temp            else          tail- gt next   temp          tail   temp           void displayNode         cout  lt  lt    nDisplay Function n       Node  temp   head      for Node  temp   head  temp    NULL  temp   temp- gt next          cout  lt  lt  temp- gt num  lt  lt          void deleteNode          for  Node  temp   head  temp    NULL  temp   temp- gt next          delete head     int main          AddnodeAtbeggining        addnodeAtend        displayNode        deleteNode        displayNode

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Below is a sample linkedlist        include  lt string gt       include  lt iostream gt       using namespace std        template lt class T gt      class Node           public          Node            Node const T amp  item  Node lt T gt   ptrnext   NULL           T value          Node lt T gt    next              template lt class T gt      Node lt T gt   Node                 value   NULL          next   NULL            template lt class T gt      Node lt T gt   Node const T amp  item  Node lt T gt   ptrnext   NULL                this- gt value   item          this- gt next   ptrnext             template lt class T gt      class LinkedListClass           private          Node lt T gt    Front          Node lt T gt    Rear          int Count      public          LinkedListClass             LinkedListClass            void InsertFront const T Item           void InsertRear const T Item           void PrintList               template lt class T gt      LinkedListClass lt T gt   LinkedListClass                 Front   NULL          Rear   NULL             template lt class T gt      void LinkedListClass lt T gt   InsertFront const T  Item                if  Front    NULL                        Front   new Node lt T gt                 Front- gt value   Item              Front- gt next   NULL              Rear   new Node lt T gt                 Rear   Front                    else                       Node lt T gt    newNode   new Node lt T gt                 newNode- gt value   Item              newNode- gt next   Front              Front   newNode                       template lt class T gt      void LinkedListClass lt T gt   InsertRear const T  Item                if  Rear    NULL                        Rear   new Node lt T gt                 Rear- gt value   Item              Rear- gt next   NULL              Front   new Node lt T gt                 Front   Rear                    else                       Node lt T gt    newNode   new Node lt T gt                 newNode- gt value   Item              Rear- gt next   newNode              Rear   newNode                      template lt class T gt      void LinkedListClass lt T gt   PrintList                 Node lt T gt     temp   Front          while  temp- gt next    NULL                        cout  lt  lt       lt  lt  temp- gt value  lt  lt                  if  temp    NULL                                temp    temp- gt next                             else                               break                                     int main                 LinkedListClass lt int gt    LList   new LinkedListClass lt int gt             LList- gt InsertFront 40           LList- gt InsertFront 30           LList- gt InsertFront 20           LList- gt InsertFront 10           LList- gt InsertRear 50           LList- gt InsertRear 60           LList- gt InsertRear 70           LList- gt PrintList

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link list by using node class and linked list class this is just an example not the complete functionality of linklist  append function and printing a linklist is explained in the code code    include lt iostream gt  using namespace std   Node class class Node      public      int data      Node  next NULL      Node int data                        this- gt data data                         link list class named as ll class ll      public          Node  head   ll Node  node                this- gt head node         void append int data                Node  temp this- gt head          while temp- gt next  NULL                                temp temp- gt next                        Node  newnode  new Node data              newnode- gt data data          temp- gt next newnode        void print list           cout lt  lt endl lt  lt  quot printing entire link list quot  lt  lt endl          Node  temp  this- gt head          while temp- gt next  NULL                                cout lt  lt temp- gt data lt  lt endl                  temp temp- gt next                        cout lt  lt temp- gt data lt  lt endl              main function int main       cout lt  lt  quot hello this is an example of link list in cpp using classes quot  lt  lt endl    ll list1 new Node 1      list1 append 2     list1 append 3     list1 print list         thanks      screenshot https   i stack imgur com C2D9y jpg

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I think that  to make sure the indeep linkage of each node in the list  the addNode method must be like this   void addNode struct node  head  int n      if  head- gt Next    NULL        struct node  NewNode   new node      NewNode- gt value   n      NewNode- gt Next   NULL      head- gt Next   NewNode        else      addNode head- gt Next  n

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Here is my implementation    include  lt iostream gt   using namespace std   template lt  class T gt  struct node      T m data      node  m next node       node T t data  node  t node            m data t data   m next node t node          node            std  cout  lt  lt   Address     lt  lt  this  lt  lt    Destroyed   lt  lt  std  endl            template lt class T gt  class linked list   public      node lt T gt   m list       linked list    m list nullptr         void add node T t data            node lt T gt    new node   new node lt T gt  t data  nullptr            new node- gt m next node   m list          m list    new node              void populate nodes node lt T gt   t node            if   t node    nullptr                std  cout  lt  lt   Data     lt  lt  t node- gt m data                        lt  lt     Address     lt  lt  t node- gt m next node                        lt  lt  std  endl              populate nodes t node- gt m next node                        void delete nodes node lt T gt   t node            if  t node    nullptr                delete nodes t node- gt m next node                     delete t node               int main         linked list lt float gt    ll   new linked list lt float gt           ll- gt add node 1 3        ll- gt add node 5 5        ll- gt add node 10 1        ll- gt add node 123        ll- gt add node 4 5        ll- gt add node 23 6        ll- gt add node 2         ll- gt populate nodes  ll- gt m list         ll- gt delete nodes  ll- gt m list        delete  ll        return 0

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This is the most simple example I can think of in this case and is not tested  Please consider that this uses some bad practices and does not go the way you normally would go with C    initialize lists  separation of declaration and definition  and so on   But that are topics I can t cover here   include  lt iostream gt  using namespace std   class LinkedList         Struct inside the class LinkedList        This is one node which is not needed by the caller  It is just        for internal work      struct Node           int x          Node  next             public member public         constructor     LinkedList            head   NULL     set head to NULL               destructor      LinkedList            Node  next   head                   while next                    iterate over all elements             Node  deleteMe   next              next   next- gt next         save pointer to the next element             delete deleteMe           delete the current entry                             This prepends a new value at the beginning of the list     void addValue int val           Node  n   new Node         create new Node         n- gt x   val                 set value         n- gt next   head             make the node point to the next node                                      If the list is empty  this is NULL  so the end of the list -- gt  OK         head   n                   last but not least  make the head point at the new node                returns the first element in the list and deletes the Node         caution  no error-checking here      int popValue            Node  n   head          int ret   n- gt x           head   head- gt next          delete n          return ret            private member private      Node  head     this is the private member variable  It is just a pointer to the first Node     int main         LinkedList list       list addValue 5       list addValue 10       list addValue 20        cout  lt  lt  list popValue    lt  lt  endl      cout  lt  lt  list popValue    lt  lt  endl      cout  lt  lt  list popValue    lt  lt  endl         because there is no error checking in popValue    the following        is undefined behavior  Probably the program will crash  because        there are no more values in the list         cout  lt  lt  list popValue    lt  lt  endl      return 0     I would strongly suggest you to read a little bit about C   and Object oriented programming  A good starting point could be this  http   www galileocomputing de 1278 GPP opoo EDIT  added a pop function and some output  As you can see the program pushes 3 values 5  10  20 and afterwards pops them  The order is reversed afterwards because this list works in stack mode  LIFO  Last in First out

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You should take reference of a head pointer  Otherwise the pointer modification is not visible outside of the function   void addNode struct Node   amp head  int n       struct Node  NewNode   new Node   NewNode- gt  x   n   NewNode - gt  next   head   head   NewNode

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In a code there is a mistake   void deleteNode          for  Node   temp   head  temp    NULL  temp   temp- gt  next          delete head      It is necessary so   for    head    NULL          Node  temp   head      head   temp- gt next       delete temp

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The addNode function needs to be able to change head  As it s written now simply changes the local variable head  a parameter    Changing the code to  void addNode struct Node   amp  head  int n               would solve this problem because now the head parameter is passed by reference and the called function can mutate it

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I ll join the fray   It s been too long since I ve written C   Besides  there s no complete examples here anyway   The OP s code is basically C  so I went ahead and made it work with GCC     The problems were covered before  the next pointer wasn t being advanced   That was the crux of the issue     I also took the opportunity to make a suggested edit  instead of having two funcitons to malloc  I put it in initNode   and then used initNode   to malloc both  malloc is  the C  new  if you will    I changed initNode   to return a pointer    include  lt stdlib h gt   include  lt stdio h gt      required to be declared before self-referential definition struct Node   struct Node       int x      struct Node  next      struct Node  initNode  int n       struct Node  head   malloc sizeof struct Node        head- gt x   n      head- gt next   NULL      return head     void addNode struct Node   head  int n    struct Node  NewNode   initNode  n     NewNode - gt  next    head    head   NewNode     int main int argc  char  argv          struct Node  head   initNode 5       addNode  amp head 10       addNode  amp head 20       struct Node  cur    head      do           printf  Node    p    i n   void  cur  cur- gt x          while     cur   cur- gt next      NULL         compilation  gcc -o ll ll c  output   Node   0x9e0050   20 Node   0x9e0030   10 Node   0x9e0010   5

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