Please help me find where my code fails and why. I'm trying to insert nodes at the front in the linked list.I don't know where I'm going wrong.

Question

1.50/5 (2 votes)

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C#

#include<iostream>
using namespace std;
class A
{
typedef struct node
{
public:
int data;
node *next;
};
node *head;
head=(node*)malloc(sizeof(node));
head=NULL;
public void createNode()
{
for(int i=1;i<4;i++)
{
node *temp;
temp=(node*)malloc(sizeof(node));
temp->data=i;
temp->next=head;
head=temp;
}
}
public void display()
{
for(int i=1;i<4;i++)
{
node *temp1;
temp1=(node*)malloc(sizeof(node));
temp1=head;
cout<<temp1->data<<"->";
temp1=temp1->next;
}
}
};
int main()
{
for(int i=1;i<=3;i++)
{
A ob[i];
ob[i].createNode();
}
A ob1;
ob1.display();
}

Posted 17-Jul-14 10:05am

AbinayaThiyagarajan

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Comments

nv3 18-Jul-14 3:28am

Your code does not compile. The line "node *head;" is outside any member function in class A. Give it a little more attention before you turn in your homework for others to do.

AbinayaThiyagarajan 18-Jul-14 9:20am

Thank you.Btw this is not homework,I'm just practising.

2 solutions

Solution 1

Well, your main makes little sense. Try:

C++

int main()
{
  A ob[3];
  // create 3 identical lists of 4 nodes
  for(int i = 1; i <= 3; i++)
  {
    ob[i-1].createNode();
  }

  ob[0].display();
}

Posted 17-Jul-14 10:15am

Matt T Heffron

Comments

AbinayaThiyagarajan 17-Jul-14 16:18pm

Still its showing error at the place where head node is initially created ! :/

Matt T Heffron 17-Jul-14 16:26pm

The main was so bad I didn't look at the rest!
Your head initialization code isn't even in a function!
Don't create a head node.
The head should be NULL until there's something in the list.
display() should NEVER be malloc-ing a new node.
The first 2 lines (after removing the line with malloc) of the body of the for loop there should be before the for statement.
And the for statement should be while (temp1 != NULL)

AbinayaThiyagarajan 17-Jul-14 16:34pm

Its very confusing.
To display the nodes ,i need to traverse.For traversing ,i need a new pointer of type node in my display function.
Without malloc-ing how will i allocate memory?? O_o
will you please edit the code and show me?
In the meanwhile, I will also try to debug.

Matt T Heffron 17-Jul-14 17:11pm

You've declared the node* (temp1).
Just assign to it.
You don't need to create an object of the target of the pointer before you can use the pointer.
In fact, what you have leaked the memory of the malloc-ed nodes in display()!

This looks very much like class-related work, so I'm not going to do it for you, but I'll try to point you in the right direction.

AbinayaThiyagarajan 17-Jul-14 22:05pm

Errr,Thank you anyways. But this is not class related work,I'm preparing for my placements.Basically I'm allergic to pointers and linked lists but this was the first time i tried on my own after reading the article.

Matt T Heffron 18-Jul-14 13:20pm

This is what I suggested above:
public void display()
{
node *temp1;
temp1 = head;
while (temp1 != NULL)
{
cout << temp1->data << "->";
temp1=temp1->next;
}
}

AbinayaThiyagarajan 19-Jul-14 0:10am

Thanks a ton, Dear Matt T Heffron ! I have tried based on your suggestion. but still i have one extra "->" arrow which gets printed whenever i call display.how to get rid of it? Any suggestion?

Matt T Heffron 21-Jul-14 13:07pm

Yes, a couple.
But first you should think about what should be displayed if display() is called for an empty list.
That is a "special case" you'll need to handle.
For the trailing "->" issue.
Try making it a prefix when printing:
public void display()
{
node *temp1;
temp1 = head;
char* prefix = ""; // initially empty (no prefix to first element)
while (temp1 != NULL)
{
cout << prefix << temp1->data;
temp1=temp1->next;
prefix = "->"; // for all of the remaining elements, use the arrow prefix
}
}

AbinayaThiyagarajan 23-Jul-14 8:34am

Yeah will try it and let you know when its correct.

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AbinayaThiyagarajan · Accepted Answer · 2014-07-18T18:07:00

Solution 3

C#

#include<iostream>
using namespace std;
 struct node{
    int data;
    struct node* next;
};

struct node* insertFront(struct node *head,int k){
    node* newnode=new node;
    newnode->data=k;
    newnode->next=head;
    head=newnode;
    return head;
}
void display(struct node *head1){
    node *temp;
    temp=head1;
    while(temp!=NULL){
    cout<<temp->data<<"->";
    temp=temp->next;
    }
}
int main(){
     struct node *head=new node;
     head=NULL;
     head=insertFront(head,5);
     head=insertFront(head,6);
     display(head);
    }

Posted 18-Jul-14 18:07pm

AbinayaThiyagarajan

Comments

nv3 20-Jul-14 17:25pm

Fine that you finally found the solution to your question. But why did you post it in the first place if it was so easy to solve it by yourself? And then even post two solutions? Are you kidding us?

AbinayaThiyagarajan 21-Jul-14 8:40am

If u don't want to help ,just leave.

AbinayaThiyagarajan 21-Jul-14 8:42am

Go read the terms and policy of the site where u created the account.Its my right to ask doubts,to post solution when i find the answer.did i ask u specifically ?? or did u spend too much time to point out the errors?? DON'T WRITE COMMENTS JUST FOR THE SAKE OF WRITING.