Program crashes while adding a new node in linked list in c++

Question

I am trying to implement an insert function of the linked but as soon as I add the third element the program just crashes and execution is stopped, even though the same code worked on hackerrank's compiler.

Here is my code.

#include<bits/stdc++.h>
using namespace std;
class Node{
 public:
 int data;
 Node * next;
 Node(int data){
 this -> data = data;
 this -> next = nullptr;
 }
};
Node * insert_tail(Node * head, int data){
 Node * node = new Node(data);
 if(head == nullptr) return node;
 Node * current = head;
 while(head -> next != nullptr) current = current -> next;
 current -> next = node;
 return head;
}
void print_linkedlist(Node * head){
 while(head -> next != nullptr){
 cout << head -> data << " -> ";
 head = head -> next;
 }
 cout << head -> data << " -> nullptr";
}
int main(){
 Node * head = nullptr;
 head = insert_tail(head, 1);
 head = insert_tail(head, 5);
 head = insert_tail(head, 3);
 head = insert_tail(head, 5);
 head = insert_tail(head, 8);
 head = insert_tail(head, 17);
 print_linkedlist(head);
 return 0;
}

• eerorika: Which line does the execution crash on?
• JHBonarius: You should learn to use a debugger and step through the code to see what's happening.
• Shaikh Abuzar: Sorry about that I added the definition, but as @MikeCAT mentioned it was a logical error.
• Shaikh Abuzar: I am new to C++ can you send me some tutorial on how to use debugger.
• user4581301: Tactical note: Loops like while(head -> next != nullptr) are risky and require additional tests to ensure that head is valid before the first head -> next. I usually find it better to write while(head != nullptr) and build the initial test into the loop.

Answer 1

The line

 while(head -> next != nullptr) current = current -> next;

in the function insert_tail is wrong. It will run endlessly when head->next is not nullptr.

It should be

 while(current -> next != nullptr) current = current -> next;

Answer 2

Here is a typo

while(head -> next != nullptr) current = current -> next;
 ^^^^^^^^^^^^

Write

while(current -> next != nullptr) current = current -> next;
 ^^^^^^^^^^^^

An alternative definition of the function can look the following way,

void insert_tail( Node * &head, int data )
{
 Node **current = &head;
 while ( *current ) current = &( *current )->next;
 *current = new Node( data );
}

And the function can be called simply like

insert_tail(head, 1);

Also the function print_linkedlist can be written like

std::ostream & print_linkedlist( const Node * head, std::ostream &os = std::cout )
{
 for ( ; head; head = head->next )
 {
 os << head -> data << " -> ";
 }
 return os << "nullptr";
}

and can be called like

print_linkedlist(head) << '\n';