How to reverse a singly linked list in C++? - c++

Question

I am trying to reverse a single linked list with this code but its not working properly.The following code not works in that case when the size of list is two otherwise it works well.I cannot find error in this code and spent a lot of time on it.Please tell me whats wrong with this code?
void list::reverse()
{
node *current = head;
if (current->next != NULL)
{
node *move = current->next;
while (move->next != NULL)
{
node *temp = move->next;
move->next = current;
if (current == head)
{
current->next = NULL;
}
current = move;
move = temp;
}
if (move->next == NULL)
{
move->next = current;
if (current == head)
{
current->next == NULL;
}
head = move;
}
}
}

Answer 1

You have:
A (== head) -> B -> C -> D
You want (?):
D (== head) -> C -> B -> A
I got lost in your algorithm completely, can't figure out how it would work, or how to fix it easily. Actually I have hard time to believe it works for longer lists. But too lazy to try.
Maybe try to understand this one (in pseudo C++), looks simpler to me?:
src = head;
reversed = nullptr;
while (nullptr != src) {
// node to insert at the beginning of reversed list
to_prepend = src;
// iterate trough all nodes in normal direction
src = src->next;
// now insert the currently read node at the head of reversed list
to_prepend->next = reversed;
reversed = to_prepend;
}
head = reversed;
I didn't wrote code+debug, so can't guarantee correctness, but it should work like this:
A (== head) -> B -> C -> D
current: A, reversed null, current updated to B (A->B), A->reversed(nullptr), reversed=A
current: B, reversed A, current to C (B->C), B->reversed(A), reversed=B
current: C, reversed B->A, current to D, C->reversed(B), reversed=C
current: D, reversed C->B->A, current to nullptr, D->reversed(C), reversed=D
current: nullptr: exit while
head = reversed (= D->C->B->A->nullptr).
Also in your code the:
current->next == NULL; is boolean expression, throwing the result away, not doing anything.