Deleting first element of a linked list

[sara]

Hi All,

I am creating a linked list (containing numbers 0 to 10) and want to
delete the first element of the list (0) but the result is not
correct. Could you please help?

Thanks a lot
Sara

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>

using namespace std;

struct node
{
node* next;
int data;
};

void PrintList(node *head)
{
while (head)
{
cout<<head->data<<" ";
head=head->next;
}
}

void DeleteNode(node* head,int i)
{
if (!head)
return;

if (head->data==i)
{
node *tmp=head;
head=head->next;
delete tmp;
return;
}
}

int main()
{
node *head=NULL;
for (int i=10; i>=0;i--)
{
node* n=new node;
n->data=i;
n->next=head;
head=n;
}

DeleteNode(head,0);
PrintList(head);

return 0;
}

 

[Michael Doubez]

Hi All,

I am creating a linked list (containing numbers 0 to 10) and want to
delete the first element of the list (0) but the result is not
correct. Could you please help?

Thanks a lot
Sara

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>

using namespace std;

struct node
{
        node* next;
        int data;

};

void PrintList(node *head)
{
        while (head)
        {
                cout<<head->data<<" ";
                head=head->next;
        }

}

void DeleteNode(node* head,int i)

Here you pass head by value, you should pass it by reference:
void DeleteNode(node*& head,int i)

 

[sara]

Here you pass head by value, you should pass it by reference:
void DeleteNode(node*& head,int i)

Thanks but why it can delete a node in the middle if I pass by value??

 

[sara]

(e-mail address removed):











There was no code in your example deleting in the middle.

The problem with head was that there is a local pointer 'head' in the
main() function. If you delete the node this pointer points to, you have
to update this pointer value in main() somehow. There are several ways to
do that, passing by reference is just one of them.

hth
Paavo

The following code delete the node in the middle but not at the first!

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>

using namespace std;

struct node
{
node* next;
int data;
};

void PrintList(node *head)
{
while (head)
{
cout<<head->data<<" ";
head=head->next;
}
}

void DeleteNode(node* head,int i)
{
if (!head)
return;

if (head->data==i)
{
node *tmp=head;
head=head->next;
delete tmp;
return;
}

while (head->next)
{
if (head->next->data==i)
{
node *tmp=head->next;
head->next=head->next->next;
delete tmp;
return;
}
head=head->next;
}
}

int main()
{
node *head=NULL;
for (int i=10; i>=0;i--)
{
node* n=new node;
n->data=i;
n->next=head;
head=n;
}

DeleteNode(head,0);
PrintList(head);

return 0;
}

 

[Michael Doubez]

The following code delete the node in the middle but not at the first!

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>

using namespace std;

struct node
{
        node* next;
        int data;

};

void PrintList(node *head)
{
        while (head)
        {
                cout<<head->data<<" ";
                head=head->next;
        }

}

void DeleteNode(node* head,int i)

You forgot the reference.

{
        if (!head)
                return;

The usual pattern uses pointer pointer:
for( node ** it = &head; *it ; it = &((*it)->next) )
// ... rest is left as an exercise