Linked List

[cvp9148]

Hi, I am implementing a simple linked list....Any idea why my print function is not working?

#include <iostream>
#include<stdio.h>
using namespace std;

struct litem {
int data;
litem* next;
}*head=NULL;

void insert_item(int val)
{
litem *temp,*tmp;
if(head==NULL)
{
head = new litem;
head->data=val;
head->next=NULL;
}
temp=head;
if (temp!=NULL){

while(temp->next!=NULL)
{temp=temp->next;}
temp=new litem;
temp->data=val;
temp->next=NULL;
cout<<temp->data;

}

}
void print(){
litem *temp2;
temp2=head;
while(temp2->next!=NULL){
cout<<temp2->data;
temp2=temp2->next;
}
}
int main()
{

insert_item(3);
insert_item(2);
insert_item(1);
print();
return 0;
getchar();
}

[mloutris]

Hi,

I copied your code into a code blocks project and I am seeing that you get to print() and you are successfully setting temp2 to head.
The problem is that temp2->next is NULL (and therefore so is head->next.
There must be an issue with your insert function.
I'll take a look now.

-Mike

[cvp9148]

Thank u for replying...

[vlad from moscow]

This function

void insert_item(int val)
{
litem *temp,*tmp;
if(head==NULL)
{
head = new litem;
head->data=val;
head->next=NULL;
}
temp=head;
if (temp!=NULL){

while(temp->next!=NULL)
{temp=temp->next;}
temp=new litem;
temp->data=val;
temp->next=NULL;
cout<<temp->data;

}

is invalid. Consider the case when head == NULL. You always will have only one element pointed to by header because you always overwrite temp..


EDIT: the correct code can look the following way

void insert_item( int val )
{
l  if ( head == NULL )
   {
      head = new litem;
      head->data = val;
      head->next=NULL;
      return;
   }

   item *temp = head;
 
   while ( temp->next != NULL )
   { 
      temp=temp->next;
   }

   temp->next = new litem;
   temp->next->data = val;
   temp->next->next = NULL;
}

Though it would be better to define a constructor in class Item. For example

struct litem 
{
   litem( int val ) : data( val ), next( 0 ) {}   
   int data;
   litem* next;
} *head=NULL

[cvp9148]

ok, so what do i change to get it to work? do i reassign temp to head later on in the code...thanks for replying

[mloutris]

It appears to me that in line 20 below, you are allocating a new struct and assigning it to temp. Unfortunately, temp is not linked to head.
One way to fix this is to allocate the new struct to temp->next.

And in the future, please use the <> brackets under 'Format:' and enter your code in-between the delimiters for easier reading. ;-)

void insert_item(int val)
{
    litem *temp,*tmp;
    if(head==NULL)
    {
        head = new litem;
        head->data=val;
        head->next=NULL;
    }

    temp=head;

    if (temp!=NULL)
    {
        while(temp->next!=NULL)
        {
            temp=temp->next;
        }
                   
        temp=new litem;
        temp->data=val;
        temp->next=NULL;
        cout<<temp->data;
    }
}

[mloutris]

Vlad actually gave you the fix. In line 18 he is assigning the new item to temp->next.

[cvp9148]

Thanks for the help guys, I really appreciate it..