Deleting a specific value from singly linked list? - c++

Question

I've been trying to delete a node if the data matches a specific value.
Here's my delete value method:
void del_value(int data)
{
Node *temp = head;
int i = 0;
while(temp!=NULL)
{
if(temp->data == data)
{
del_index(i);
i--; // Since the nodes count will be reduced after deleting, reducing the index by one.
}
i++;
temp = temp->next;
}
}
And here is my del_index method(Which is working correctly):
int getCount()
{
int i = -1;
Node *temp = head;
while(temp!=NULL)
{
temp = temp->next;
i++;
}
return i;
}
void del_index(int pos)
{
int count = getCount();
if(pos == 0)
{
del_start();
}
else if(pos == count)
{
del_last();
}
else if(pos<0 || pos>count)
{
cout<<"Out of range"<<endl;
return;
}
else
{
int i = 1;
Node *temp = head;
while(i<pos)
{
temp = temp->next;
i++;
}
Node *toDel = temp->next;
Node *forward = toDel->next;
temp->next = forward;
delete toDel;
}
}
And here is my main method:
int main()
{
Mylist l;
l.add_start(4);
l.add_start(4);
l.add_start(4);
l.del_value(4);
l.show();
}
But it stucks when it reaches del_value method inside loop. Any idea where am I missing?
Update: (Added del_first and del_last methods
void del_start()
{
if(head == NULL)
{
cout<<"List is empty"<<endl;
return;
}
else
{
Node *temp = head;
head = head->next;
delete temp;
}
}
void del_last()
{
if(head == NULL)
{
cout<<"List is empty"<<endl;
return;
}
else
{
Node *temp = head;
while(temp->next != NULL)
{
tail = temp;
temp = temp->next;
}
tail->next = NULL;
delete temp;
}
}

Answer 1

Your del_value method will not work because you delete the object being pointed to by 'temp' then you dereference it after (with "temp = temp->next").
For your example code, I would cache the 'next' value before your conditional, for example:
Node *next = temp->next;
if(temp->data == data)
{
del_index(i);
i--;
}
i++;
temp = next;
I am assuming you're doing this for practice purposes but I would add the following suggestions:
I wouldn't call del_index here but remove the node inline, within the del_value method. As you have the necessary pointers to be able to remove it. del_index has to traverse your list a second time.
I would also recommend using the containers within the stl instead of rolling your own to avoid encountering issues like this.