linked list

[onyx fulcrum]

Im rn learning linked lists and therefor I wanted to make a programm visualizing the mathematical 3x+1 Problem (random number that if its even gets divided by 2 and if its odd gets multiplied by 3 and +1). The linked list should track the History of the numbers. But im struggling implemanting it correctly. Here is my code:

#include <iostream>
#include <cmath>
using namespace std;
int number;
int counter;
struct Liste_Zahlen
{
    int data;
    Liste_Zahlen* next;
};

int funktion(){
while(number != 1)
{
    if(number % 2)
    {
    number = number/2;
    }
    else
    {
    number = 3 * number + 1;
    }
    Liste_Zahlen* n;
    Liste_Zahlen* t;
    n = new Liste_Zahlen;
    t = n;
    n->data = number;
    t->next = n;
    t = t->next;
counter = counter + 1;
}
return counter;
}

int main(){

cout << "Geben Sie eine Zahl an? " <<endl;
cin >> number;
    Liste_Zahlen* n;
    Liste_Zahlen* t;
    Liste_Zahlen* h;
    n = new Liste_Zahlen;
    t = n;
    h = n;
    n->data = number;
funktion();
cout << "Die Zahl " << number << " ist nach " << counter << " Schritten in den Loop gefallen." <<endl;
cout << "Die mit dem Algorithmus erreichten Zahlen sind: " << 

    system("pause");
    return 0;
}```

[dull jetty]

When your question is answered use !solved to mark the question as resolved.

Remember to ask specific questions, provide necessary details, and reduce your question to its simplest form. For tips on how to ask a good question use !howto ask.

[kindred jasper]

You can format it with c++ syntax if you add cpp right infront of the three apostrophes

[onyx fulcrum]

thx man

[kindred jasper]

nice, now what trouble you facing?

[onyx fulcrum]

I briefly explained the mathematical part above, but I think its not that important for my problem. I want to create a linked list that hosts and prints in the end every number out for my math algorithm for example if u set number to 8, it should print out 8, 4, 2, 1.

or 5 should print out 5, 16, 8, 4, 2, 1

[kindred jasper]

yep i'm aware of this 3x + 1

my questions is, what is the outcome you are getting, vs the outcome you want

is the maths wrong? or the list not working? giving you runtime error?

[onyx fulcrum]

I didnt test it probably because my first problem is to cout the list in the end

math is right

list is not working ig

[kindred jasper]

right so you want help with the list

right first of all

You're using new but not delete -> this is a memory leak (bad)

[onyx fulcrum]

like the code is outside of the list not 100% working either but I should be capable of doing this. But yeah I need help with the list

[kindred jasper]

i think at one point

number will never be 1 again

that is an infinite loop

[onyx fulcrum]

but it stops when it hits 1 the first time right?

[kindred jasper]

right okay

[kindred jasper]

it looks like instad of creating a new node you are just overrwriting the other one

[onyx fulcrum]

oh

how can I implement it then that it creates a new node every loop in the while loop

thats like the main think what I dont understand

[kindred jasper]

I think you should try do a linked list by itself instead of implementing it using this 3x + 1 function thing

meaning using a simple node

and add to the list using a function, and monitor the amount of nodes etc...

even though its not like, "usable", you need to understand how to actually implement it first

i think this 3x + 1 is a good idea though for a linked list

[onyx fulcrum]

what do u mean with "by itself"

[kindred jasper]

Meaning do not try implement it using 3x+1

struct list
{
  int data;
  list* next_node;
};

^ keep that

[onyx fulcrum]

u mean to try to use linked list first in a more simple way to understand it better?

[kindred jasper]

exactly what i mean yes

then, you can use the conjecture thing (the 3x+1 function)

will be much easier

[onyx fulcrum]

okay I will try it

[kindred jasper]

practically, instead of giving it a usage, make it work first

to get from point A to point B you need to be at point A first :D

[onyx fulcrum]

okay that makes sense

haha

[kindred jasper]

yeah of course

keep this thread open ifyou need to ask anything else

also another suggestion try use english in code, it doesnt really matter but for some people it might be easier to read

or actually dont use german and english in the same code

use one xD

[onyx fulcrum]

but I have alr the question how is it possible to create a loop that makes a new node every loop

[kindred jasper]

how do you create a new node?

[onyx fulcrum]

hahah ye mb I should xdd

[onyx fulcrum]

I know how but only like "by foot" that I write it without loops if u know what I mean

[kindred jasper]

i do not understand what you mean by foot

Create 1 node first

add a node to a list

what i am asking you to do first is create the absolute bare minimum for a linked list

[onyx fulcrum]

okay I'll do that and will come back after that or when I will face new problems by doing it xd

but ty alr for the help

[kindred jasper]

ofc np

[dull jetty]

@onyx fulcrum Has your question been resolved? If so, type !solved :)

[onyx fulcrum]

okay im ready now

#include <iostream>
using namespace std;
int main() {
    struct Node{
        int data;
        Node* next;
    };
Node* n;
Node* t;
Node* h;
n = new Node;
t=n;
h=n;
n->data = 1;
n = new Node;
n->data = 2;
t->next = n;
t = t->next;
n = new Node;
n->data = 3;
t->next = n;


cout << "List: " << h->data << " " << t->data << " " << n->data <<endl;
    system("pause");
    return 0;
}```

The output is 1 2 3

how can I put it in a loop?

[kindred jasper]

right, you might want to create a class specificially for the linked list

and create a sort of

add_node()

function

[onyx fulcrum]

hm okay lets see if I get this

[kindred jasper]

one sec, let me ask someone more experienced to help you

[placid moon]

yeah if you want to use linked lists, make a linked lists class first

That will give you a better idea of how they work as well

[kindred jasper]

yes exactly

Node class, and the actual list class

[placid moon]

Make functions to add, remove, etc

[kindred jasper]

Remember, the node is independent from the list

[onyx fulcrum]

wait a class or a function

[placid moon]

A class for the linked list

[kindred jasper]

class

with functions in it

[onyx fulcrum]

okay

[kindred jasper]

member functions

[placid moon]

You can use a struct for the node

[onyx fulcrum]

I`ll try

[prisma crown]

how have you tried to put it in a loop?

[kindred jasper]

yes and a class for the list since you might want to have some access modifiers

[kindred jasper]

here @prisma crown

[kindred jasper]

also, here you are memory leaking

pls use delete

[prisma crown]

so what exactly was the problem?

[kindred jasper]

i think his issue was with how to actually implement it into a loop, but they didn't know how to create a linked list in the first place

[placid moon]

Yeah that's what it sounds like to me too

[onyx fulcrum]

like the original problem was that I wanted to make a linked list that stores every single number beginning with the number a user puts in that goes through the 3x+1 algorithm and cout everything in the end

[placid moon]

Gotta get an actual linked list going first

[onyx fulcrum]

if that was the question xd

[kindred jasper]

right it was

but you don't know how to make a linked list, so you should first do that

remember also, a list is just how you store the nodes, nodes and lists are different if this makes sense to you :D

[placid moon]

^ Then you can just use the linked list class, which will be easier

A linked list is made up of nodes

[kindred jasper]

yep exactly

[onyx fulcrum]

yeah so now I should implement a class with a delete and add function ?

[placid moon]

With whatever functions you need 🙂

Some sort of add and remove would be a good start

[kindred jasper]

yes. but you need to also manage memory

[kindred jasper]

you here are doing memory leaks

[plain scarab]

Pretty much, but normally called push and pop, does it need to be doubly linked or just single. Also use smart pointers not new or delete

[onyx fulcrum]

how can I detect memory leaks?

[placid moon]

valgrind

[kindred jasper]

you can't neccessarily detect them

or more or less there is no need to

[onyx fulcrum]

for my purpose only single

[kindred jasper]

but kind of, think of it like this :

whenever a new is called -> a delete must be called

[onyx fulcrum]

smart pointers?

[placid moon]

Well, whenever you're finished with that pointer, before you go out of scope

otherwise you have a dangling pointer

[kindred jasper]

yes it a bit of a more advanced thing that does it for you

[placid moon]

Or yeah smart pointers work

[kindred jasper]

the new and delete

not neccessarily advanced

[placid moon]

Another good thing to learn

They're preferred to manual memory allocation nowadays

[kindred jasper]

yeah you can definitely figure t hem out really quickly

[placid moon]

However, I will say

If you don't know manual memory allocation, it's good to learn it

[plain scarab]

std::unique_ptr

[placid moon]

So you understand how it works

[plain scarab]

It deletes itself when it goes out of scope

[onyx fulcrum]

okay so I add the data then I go on to the next Node and what do I delete from the prev?

[plain scarab]

Super easy to implement then

[onyx fulcrum]

idk it xd

[placid moon]

You should learn it

[kindred jasper]

you are having trouble visualizing it

[onyx fulcrum]

ah okay that practical

[kindred jasper]

^ when you add, it adds a new node, so you'd have 4 here

when you remove, it pops a node, so you'd have 2

using delete you can make it delete itself when it goes out of scope

[placid moon]

Also gotta track things like the head and the tail

So you have to update those when the list is changed

[plain scarab]

Using a unique_ptr not delete

[kindred jasper]

sure

it was a more verbose term

but yes

[placid moon]

They should learn manual memory allocation imo, they don't know it at all. And then they can move to smart pointers

Skipping over manual allocation is not a great idea imo

And this is a good time to learn it

[plain scarab]

No not really, that's not the point in this, the point in this is to make a linked list that works

[kindred jasper]

yes but you need to build a foundation first

you cannot learn lists without learning basic memory concepts

[placid moon]

Sure, but this is a prime time to learn it. So why not

[onyx fulcrum]

So I need for every list a head a tail with a nullptr and for example a n that moves between the nodes?

[plain scarab]

The foundation is to always use smart pointers until you literally can't

[placid moon]

I'm assuming they're going to keep coding, so knowing manual memory allocation is good

[plain scarab]

I'm not say it isn't good, just not needed for this

[placid moon]

Yes but you should still know memory allocation, and what's going on with the pointers as well

[kindred jasper]

right learn words without learning the alphabet

[placid moon]

Yeah that's true

I'm just suggesting they use this to learn it

[kindred jasper]

it is a good time to learn it

[onyx fulcrum]

and how do I learn memory allocation?

[plain scarab]

There really isn't much to learn here tho

[kindred jasper]

thats the point

but its worth it

it will take them half an hour

[onyx fulcrum]

does someone has a good yt video on that topic?

[kindred jasper]

https://www.learncpp.com/cpp-tutorial/dynamic-memory-allocation-with-new-and-delete/

Not sure if this is a great one but learncpp is generally good

[onyx fulcrum]

okay ty

[plain scarab]

Learn about it sure, then just never use it and use smart pointers instead

[onyx fulcrum]

I mean I am right now studying in University and need to learn the basic stuff and if they dont allow me to use smart pointers I will need to have some knowledge about the normal ones and the memory allocation

but thanks for the advice if I`ll be alowed to programm freely I will come back on this:D

[plain scarab]

If they don't let you use smart pointers then there is something seriously wrong with the staff there

[onyx fulcrum]

I mean the Course is named Basics of higher programm languages

maybe thats "too advanced" idk

[kindred jasper]

no its the opposite

smart pointers are higher level than manual memory management

or more abstracted is the right term i guess

[onyx fulcrum]

true

[onyx fulcrum]

I did it :D@kindred jasper

#include <iostream>
#include "Klasse.h"
using namespace std;
List::List(){
head = NULL;
current = NULL;
temp = NULL;
}
void List::addNode(int addData){
    nodePtr n = new node;
    n->next = NULL;
    n->data = addData;
    if(head != NULL)
    {
        current = head;
        while(current->next != NULL)
        {
            current = current->next;
        }
        current->next = n;
    }
    else{
        head = n;
    }
}
void List::deleteNode(int delData)
{
    nodePtr delPtr = NULL;
    temp = head;
    current = head;
    while (current != NULL && current->data != delData)
    {
        temp = current;
        current = current->next;
    }
    if(current == NULL)
    {
        cout << delData << " Die Zahl konnte nicht gefunden werden.\n";
        delete delPtr;
    }
    else{
        delPtr = current;
        current = current->next;
        temp = current;
        if(delPtr == head)
        {
            head = head->next;
            temp = NULL;
        }
        delete delPtr;
        cout << "Die Zahl " << delData << " wurde geloescht.\n";
    }
}
void List::PrintList()
{
    current = head;
    while (current != NULL)
    {
        cout << current->data << ", ";
        current = current->next;
    }
    
}```

and thats the header: ```cpp
#pragma once

class List{

private:
typedef struct node{
int data;
node* next;
}* nodePtr;

nodePtr current;
nodePtr temp;
nodePtr head;
int number;

public:
List();
void addNode(int addData);
void deleteNode(int delData);
void PrintList();
};```

Tmrw I will implement it into my programm

[kindred jasper]

there ya go @onyx fulcrum great work

just so you know, some nice things you can do

if(current == NULL)

can become:

if(!current)

and if you are doing pointer comparisons, use nullptr instead of null

[onyx fulcrum]

okay

thank you

for your help

and for the advices

[dull jetty]

@onyx fulcrum Has your question been resolved? If so, type !solved :)

[onyx fulcrum]

@kindred jasper I just made a function to check the highest data but when I execute my code it stops at the point the function gets involved. I added everything to the header and the .cpp class Thats the class.cpp: ```cpp
#include <iostream>
#include "Klasse.h"
using namespace std;
List::List(){
head = NULL;
current = NULL;
temp = NULL;
}
void List::addNode(int addData){
nodePtr n = new node;
n->next = NULL;
n->data = addData;
if(head != NULL)
{
current = head;
while(current->next != NULL)
{
current = current->next;
}
current->next = n;
}
else{
head = n;
}
}
void List::deleteNode(int delData)
{
nodePtr delPtr = NULL;
temp = head;
current = head;
while (current != NULL && current->data != delData)
{
temp = current;
current = current->next;
}
if(current == NULL)
{
cout << delData << " The number couldnt get found.\n";
delete delPtr;
}
else{
delPtr = current;
current = current->next;
temp = current;
if(delPtr == head)
{
head = head->next;
temp = NULL;
}
delete delPtr;
cout << "The number " << delData << " got deleted.\n";
}
}
void List::checkGreatest(int maxData)
{
current = head;
while(current->next != NULL)
{
if(maxData > current->data)
{
current = current->next;
}
else if(maxData < current->data)
{
maxData = current->data;
}

}
}
void List::PrintList()
{
current = head;
while (current != NULL)
{
cout << current->data << ", ";
current = current->next;
}

}``` Do u know what could be the problem?

Thats the main: ```cpp
#include <iostream>
#include <cmath>
#include "Klasse.h"
using namespace std;
int counter;
int number;
int placeholder = 1;
List lol;
int funktion(){

while(number != 1)
{
if(number % 2 == 0)
{
number = number/2;
}
else
{
number = 3 * number + 1;
}
lol.addNode(number);
counter = counter + 1;
}
return counter;
}

int main(){
cout << "Which number do you wanna check? " <<endl;
cin >> number;

funktion();
cout << "The number " << number << " is after " << counter << " steps proofed not perfect." << endl;
cout << "The highest number reached is: ";
lol.checkGreatest(placeholder);
cout << endl;
cout << "The algorithm reached in the process that many numbers: ";
lol.PrintList();

cout << endl;

system("pause");
return 0;

}```

and the header: ```cpp
#pragma once

class List{

private:
typedef struct node{
int data;
node* next;
}* nodePtr;

nodePtr current;
nodePtr temp;
nodePtr head;
int number;

public:
List();
void addNode(int addData);
void deleteNode(int delData);
void checkGreatest(int maxData);
void PrintList();
};```

thank u in advance 😄

[dull jetty]

@onyx fulcrum Has your question been resolved? If so, type !solved :)

[plain scarab]

@onyx fulcrum what is the issue?

There are a few issues, firstly don't use global variables that aren't constant.
Check greatest doesn't look quite right, you can get in an endless loop here easily. I am guessing this is the issue you are talking about.
Use nullptr not NULL. nullptr is the more C++ way
Don't use using namespace std;

[onyx fulcrum]

Ah okay ty

I'll try

[dull jetty]

@onyx fulcrum Has your question been resolved? If so, type !solved :)