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This only prints -1,2,-4

Posted on 1998-01-06
1
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Last Modified: 2010-04-02
What is wrong with this code, please make all code enhancements in a new c file..
It only prints -1,2-4 plus it doesn't seem to sort the incomming integer..


 #include <stdio.h>
 #include <stdlib.h>

 typedef struct node
 {
      int number;
      struct node *next;
 }Node;

 void additem(int a);
 void print(void);
 Node *head=NULL;

 main()
 {
      int i=0;
      int a1[5]={-1,2,-4,67,78};
      for (i=0;i<5;i++)
      {
        additem(a1[i]);
      }
      print();
}

void additem(int a)
{
  Node *curr;
  Node *new_node;
  Node *prev;
  Node *temp;

  new_node=(Node *)malloc(sizeof(Node));
  if (new_node==NULL)
  {
       printf("I am dreadfully sorry.. You don't have enough conventional memory to add the New Node\n");
       exit(1);
  }
  new_node->next=NULL;
  new_node->number=a;
  if (head==NULL)
  {
       head=new_node;
       return;
  }

  prev=NULL;
  curr=head;
  temp=NULL;
  temp=curr->next;
  while(curr->next != NULL)
  {

       if (curr->number< new_node->number&&new_node->number>temp->number)
       {
            new_node->next=temp;
            temp=new_node;
          return;
       }
       else
       {
             curr=curr->next;
             temp=curr->next;
       }
  }
  curr->next=new_node;
  return;
}

void print(void)
{
  Node *curr;
  int i=0;

  curr=head;



      if (curr==NULL)
      {
            printf("I am sorry this is an empty list..There is no data in the list\n");
            return;
      }

      while(curr != NULL)
      {
            printf("Node: [%d] = %d\n",i,curr->number);
            i++;
            curr=curr->next;
      }
}

Please rewrite the code. with /* showing why and what you did*/
0
Comment
Question by:johnm112496
1 Comment
 
LVL 2

Accepted Solution

by:
mlev earned 100 total points
ID: 1256927
There are 3 bugs here:
1. The comparison clause is incorrect, should be
if (curr->number < new_node->number && new_node->number < temp->number)
2. When inserting a new element into the middle of the list, the pointer in the previous element is not updated.
3. The special case where a new element should be placed in the head of the list is not handled.
4. Of course, this can only work if all numbers are distinct. Otherwise '<=' instead of '<' is needed.

The whole code (corrected):
#include <stdio.h>
#include <stdlib.h>

typedef struct node
  {
    int number;
    struct node *next;
  }
Node;

void additem (int a);
void print (void);
Node *head = NULL;

main ()
{
  int i = 0;
  int a1[5] =
  {-1, 2, -4, 67, 78};
  for (i = 0; i < 5; i++)
    {
      additem (a1[i]);
    }
  print ();
}

void
additem (int a)
{
  Node *curr;
  Node *new_node;
  Node *prev;
  Node *temp;

  new_node = (Node *) malloc (sizeof (Node));
  if (new_node == NULL)
    {
      printf ("I am dreadfully sorry.. You don't have enough conventional memory to add the New Node\n");
      exit (1);
    }
  new_node->next = NULL;
  new_node->number = a;
  if (head == NULL)
    {
      head = new_node;
      return;
    }

  if (new_node->number < head->number) /* this case was not handled */
    {
      new_node->next = head;
      head = new_node;
      return;
    }

  prev = NULL;
  curr = head;
  temp = NULL;
  temp = curr->next;
  while (curr->next != NULL)
    {

      if (curr->number < new_node->number && new_node->number < temp->number) /* the second comparison was inverted */
        {
          new_node->next = temp;
          temp = new_node;
          curr->next = new_node; /* this line was mising */
          return;
        }
      else
        {
          curr = curr->next;
          temp = curr->next;
        }
    }
  curr->next = new_node;
  return;
}

void
print (void)
{
  Node *curr;
  int i = 0;

  curr = head;



  if (curr == NULL)
    {
      printf ("I am sorry this is an empty list..There is no data in the list\n");
      return;
    }

  while (curr != NULL)
    {
      printf ("Node: [%d] = %d\n", i, curr->number);
      i++;
      curr = curr->next;
    }
}

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