Hello I have a problem to returned variable from my pop function. I will be happy if you could help me. The function receives a pointer to the top of the list and should return the answer but I have a problem with a pointer to the list and intger the answer.
Function Code -
int pop(Node* top)
{
Node* tmp = top;
int ans = tmp->next;
top = top->next;
delete tmp;
return ans;
}
Node -
struct Node
{
int num;
Node* next;
}
Node* top = new Node;
The line int ans = tmp->next; appears to be the source of the problem. This is attempting to take the next pointer in the node, convert it to an int, and return it. What you (almost certainly) want is to retrieve the data from the node and return that, with something like int ans = tmp->num;.
Of course, that's not saying the code is perfect otherwise (e.g., it seems to lack any attempt at checking for, not to mention dealing with, errors), but at least with that change, it stands some chance of working correctly under some (ideal) circumstances.
Usually such a function throws an exception if the stack is empty or it has undefined behaviour. I used return value 0 in case when the stack is empty.
int pop( Node * &top )
{
int value = 0;
if ( top )
{
value = top->num;
Node *tmp = top;
top = top->next;
delete tmp;
}
return value;
}
There is another approach when function poo has type void that is when it returns nothing but simply removes the element on the top.
As mentioned in my comment you should split this up to two separate functions. One to get the value, and another one to pop (remove) the Node
void pop(Node*& top) { // Note the reference. You want to change the current top node.
// ^
if ( top ) {
Node *tmp = top;
top = top->next;
delete tmp;
}
}
int& top(Node* top) {
if ( top ) {
return top->num;
}
// Throw an appropriate exception if the stack is empty
throw std::out_of_range("Stack is empty.");
}
First, you are trying to delete tmp node, but top node still exist and value has to be returned as ans or top->next or in this situation top->num. Why do you initialize node tmp in the function when node tmp is a parameter? Why should node * &top be in the function parameters instead of tmp.
value = top->num doesn't fix the problem, because he wants the pointer from the top of the linked list not the random node inputed through the function parameters. To fix this problem Node * tmp should equal top and then value should be equal to tmp->num. Otherwise all other problems have been fixed.
//EDIT
Ignore everything before //edit because all that is questions about his question that I now already know. I have compiled this code and it completely worked for me.
struct Node
{
int data;
Node *next;
};
int pop(Node *head)
{
while(head->next != NULL)
{
head = head->next;
}
int value;
Node *tmp;
tmp = new Node;
value = head->data;
tmp = head;
delete tmp;
return value;
}
Compiled code link - http://ideone.com/7EgBhf
