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I created a class binary search tree.
but the problem is when i print the tree it crashes.
i think it can be an endless recursion in function print().
Here is my code
struct node{
node *l,*r;
int data;
};
class BinTree
{
private: node *root;
public:
BinTree(){ root=NULL; }
void add(int a){ add_node(a,root); };
void add_node(int a, node *rot)
{ node *curr; curr=rot;
if(curr==NULL)
{
curr=new node;
curr->data=a;
curr->l=NULL;
curr->r=NULL;
return;
}
if(a>=curr->data) curr=curr->r,add_node(a,curr);
if(a<curr->data) curr=curr->l,add_node(a,curr);
}
void print(){ inorder(root); }
void inorder(node *curr)
{
if(curr->l!=NULL) inorder(curr->l);
cout<<curr->data<<" ";
if(curr->r!=NULL) inorder(curr->r);
}
};
Can anyone help me?
In your add_node method, you never actually assign a value to the root. It should be something like this:
if(curr==NULL)
{
curr=new node;
curr->data=a;
curr->l=NULL;
curr->r=NULL;
root = curr;
return;
}
But, for the future, I have the same advice as Basile - use your compiler and your debugger to your advantange.
Your add_node is broken. If curr is NULL, it creates a new node but it never actually adds it to the existing tree. Thus all additions you make are effectively ignored and the tree stays empty.
The inorder function dereferences curr without checking whether it is NULL, and print calls it without checking whether root is NULL. Thus, your crash most likely is caused by tryin to print out an empty tree and then dereferencing a null pointer.
Learn how to use a debugger. Enable all warnings in the compiler.
On Linux, this means compile with g++ -Wall -g and debug with gdb
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class node{
public:
int data;
node* next;
node(int val){
data=val;
next=NULL;
}
};
For this class, the object creation statement is node* n=new node(5);
Why do we need to add the * after node? What will happen if I write node n=new node(5)?
Are they both the same?
Why do we need to add the * after node?
new returns a pointer to the memory that was allocated, in this case a node instance, so you need a (node*) pointer variable to receive the returned memory address (of the node instance).
What will happen if I write node n=new node(5)?
The code will fail to compile, since n is not a (node*) pointer.
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I am trying to create a singly linked list by inserting nodes at end, and despite having no errors I am unable to print my linked list. Please help me debug my code.
I tried online compiler on codechef and it shows SIGSEGV Runtime error. What is this supposed to mean?
struct node
{
int data;
struct node *next;
};
void insert(struct node *root,int data)
{
struct node *temp=new(struct node);
if(root==NULL)
{
temp->data=data;
temp->next=NULL;
}
root->next=temp;
temp->data=data;
temp->next=NULL;
}
void print(struct node *root)
{
struct node *temp;
temp=root;
while(temp!=NULL)
{
cout<<temp->data;
temp=temp->next;
}
}
int main()
{
struct node *root=NULL;
insert(root,1);
insert(root,2);
insert(root,3);
insert(root,4);
print(root);
return 0;
}
Please help me debug my code.
OK lets try a dry run.
Imagine your list is empty and you are inserting your first item. So root equals NULL and we call insert.
1) first thing
struct node *temp=new(struct node);
You allocate a new node, and set temp equal to it, so far so good.
2) next thing
if(root==NULL)
this is true as explained in the preamble, so we enter the if statement
3) next thing
temp->data=data;
temp->next=NULL;
these statements in the if body get executed and initialise the newly allocated object. It's not clear why you only want to do this when root == NULL, I would think you would want to initialise the newly allocated node always. But anyway, so far no errors.
4) next thing
root->next=temp;
Now here's the error. Ask yourself, what is the value of root at this point? When we started it was NULL, has anything changed it since? The answer of course is no, so you are dereferencing a NULL pointer. That explains the error.
You need to be able to look at the code you've written and see it for what it really does. The ability to dry run your code like I did above is a very valuable skill to have.
Unfortunately your code really is not very close to being correct. So I think the best thing would be to look at some working code and see how it operates and then start again.
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Why my code is giving an Infinite loop and i have checked my code many times and I don't know where the mistake is but my output is 34 in an infinite loop and it is a code for doubly linked list!
So please tell me where the mistake is as well as why my loop is showing 34 instead of 77 in my code and is there any problem in my print function?
#include<iostream>
using namespace std;
struct Node
{
int data;
Node *next;
Node *prev;
};
class Linked
{
public:
Node *head;
Node *tail;
Linked()
{
head=NULL;
tail=NULL;
}
void add(int data,int position)
{
Node *n=new Node;
Node *n1=new Node;
n->data=data;
n->next=NULL;
n->prev=NULL;
if(head==NULL)
{
head=n;
tail=n;
cout<<"Linked list formed"<<endl;
}
if(position==0)
{
head->prev=n;
n->next=head;
head=n;
cout<<"Linked list created"<<endl;
}
else
{
n1=head;
int posi=position;
while(posi>1)
{
n1=n1->next;
posi--;
}
n->next=n1->next;
n->next->prev=n;
n1->next=n;
n->prev=n1;
}
}
void print()
{
Node *n=new Node;
n=head;
while(n!=NULL)
{
cout<<n->data<<endl;
n=n->next;
}
}
};
int main()
{
Linked l;
l.add(34,0);
l.add(77,0);
// l.add(44,1);
// l.add(90,2);
l.print();
return 0;
}
add (data,position) has 2 problems.
For the very first node in Doubly Linked List , once head and tail are pointed to the same node, we are done. Position do not matter, when there is no node.
So stop add logic after "Linked List Formed". Add Else and move rest all code inside, It works as expected.
Code should be able to assert Head-> Prev and Tail-> next to be null.
Also while adding a single new node, you do not want to allocate memory for 2x Nodes.
Do not call new Node () for n1.
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I'm a computer science student and have been coding with Java for the past year. Now I'm interested in learning C++. The first program that I wanted to code with C++ is an implementation of stack using linked list, which I have coded before using java. I pretty much have no idea what I'm doing and basically just writing what I thought was right until I got no compile error. So I finally did it, my program got no compile error, but when I ran it, a pop-up appeared saying that my 'Stack.exe has stopped working'
Here's my code:`
#include <iostream>
using namespace std;
class Stack;
class Node;
class Node
{
public:
string element;
Node *next;
Node(string, Node);
};
Node::Node(string element, Node next)
{
this -> element = element;
*(this -> next) = next;
}
class Stack
{
private:
Node *tos;
public:
Stack()
{
tos = NULL;
}
void push(string str)
{
tos = new Node(str, *tos);
}
string peek()
{
return tos->element;
}
string pop()
{
string temp = tos->element;
tos = (tos->next);
return temp;
}
};
int main(void)
{
Stack bob;
bob.push("Wow");
bob.push("Wiw");
cout << bob.peek();
return 0;
}
Can someone tell me what I did wrong? I did it like this because this was how I did it with Java.
Thank you :D
You're dereferencing null or undefined pointers in a couple places. First let's look at your Node constructor:
*(this -> next) = next;
Since next hasn't been defined yet, dereferencing it leads to undefined behavior. In practice, next will point to some random place in memory that you probably don't own, so writing to it will cause a program crash. Your Node constructor should take a pointer to Node as its second parameter instead of taking a Node by value:
Node::Node(string element, Node* next)
: element{element},
next{next}
{}
Note that I've also initialized Node's members instead of default-initializing them and then assigning to them in the constructor's body.
After fixing Node's constructor, you'll also need to fix Stack::push to pass a pointer instead of an object:
void push(string str)
{
tos = new Node(str, tos);
}
Note that even after fixing the crashing problem, you'll still leak memory when you pop from your Stack (or when a Stack is destroyed). You need to delete anything you new, or better yet use std::shared_ptr<Node> instead of raw Node*s.
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I wrote a doubly linked list, and trying to add an append()(insert at the end)and len()(caculate the number of member in the list). I just don't understand why it doesn't work now. Here is the simplest code:
#include<iostream>
using namespace std;
class linkedList{
private:
struct node{
node* last;
node* next;
char* str;
};
node sentinel;
public:
linkedList();
~linkedList();
int len();
void append(char*);
};
linkedList::linkedList(){
sentinel.last=&sentinel;
sentinel.next=&sentinel;
sentinel.str="I am sentinel!!";
};
linkedList::~linkedList(){};
int linkedList::len(){
node* currentNode=&sentinel;
int count=0;
while ((*currentNode).next!=&sentinel){
count++;
currentNode=(*currentNode).next;
cout<<(*currentNode).str<<endl;
}
return count;
}
void linkedList::append(char* str){
node newNode;
newNode.str=str;
newNode.last=sentinel.last;
(*sentinel.last).next=&newNode;
sentinel.last=&newNode;
newNode.next=&sentinel;
}
int main(){
linkedList myList;
myList.append("Hello");
myList.append("World");
int length=myList.len();
cout<<length<<endl;
return 0;
}
What I am doing is just add two new nodes into the linked list, and caculate the total number of my nodes. it should return 2. but why it doesn't work?
newNode in your code below will go out of scope as soon as append is finished executing. Assigning it's memory address as a pointer to more global member is likely going to end in a segfault.
void linkedList::append(char* str){
node newNode;
newNode.str=str;
newNode.last=sentinel.last;
(*sentinel.last).next=&newNode;
sentinel.last=&newNode;
newNode.next=&sentinel;
}
Try allocating your node on the heap using new node, possibly using a shared_ptr to make memory management a bit simpler.
void linkedList::append(char* str){
node *newNode = new node;
newNode->str=str;
newNode->last=sentinel.last;
(*sentinel.last).next=newNode;
sentinel.last=newNode;
newNode->next=&sentinel;
}
With this approach, be sure to cleanup the nodes when destructing your linkedlist, via the delete operator on each node.
Alternatively, look into using shared_ptr's to a Node instead of raw pointers, which will always call delete when the linkedlist (and nobody else) is pointing to the node.
Use the new keyword to allocate a new node:
void linkedList::append(char* str){
node *newNode = new node();
newNode->str=str;
newNode->last=sentinel.last;
(*sentinel.last).next=newNode;
sentinel.last=newNode;
newNode->next=&sentinel;
}