C++ linked list with too many pointers

Question

Can someone tell me how I can improve this code? It works ok, but I feel that I'm using too many pointers.

#include <iostream>
using namespace std;
struct link{
 int data;
 link *next;
};
class link_list{
private:
 int boundaries = 0;
 link *tail;
 link *temp;
 link *head = NULL;
public:
 void add_node(int data){
 temp = new link;
 temp->data = data;
 temp->next = NULL;
 if (head == NULL){
 head = temp;
 boundaries++;
 }
 else{
 link *tail = head;
 while (tail->next != NULL){
 tail = tail->next;
 }
 tail->next = temp;
 boundaries++;
 }
 }
 void delete_b(){
 link *end = head;
 link *next_to_end = NULL;
 while (end->next != NULL){
 next_to_end = end;
 end = end->next;
 }
 next_to_end->next = NULL;
 end = NULL;
 boundaries--;
 }
 void add_front(int data){
 link *ptr = new link;
 ptr->next = head;
 ptr->data = data;
 head = ptr;
 boundaries++;
 }
 void delete_front(){
 link *new_head = head;
 new_head = head->next;
 head = NULL;
 head = new_head;
 boundaries--;
 }
 void add_by_position(int data, int pos){
 link *node = new link;
 link *linker = head;
 node->data = data;
 for (int i = 0; i < pos; i++){
 linker = linker->next;
 }
 node->next = linker;
 linker = head;
 for (int i = 0; i < pos - 1; i++){
 linker = linker->next;
 }
 linker->next = node;
 boundaries++;
 }
 void show(){
 link *sh = head;
 while (sh){ cout << sh->data << endl; sh = sh->next; }
 }
};
int main()
{
 link_list obj;
 obj.add_node(7);
 obj.add_node(5);
 obj.add_node(8);
 obj.show();
}

Answer 1

struct link{
 int data;
 link *next;
};

Are you sure you want this to be outside of the class? This could be in the private section in the class link_list since the outside world does not need to know of this class at all.

---

int boundaries = 0;

What is boundaries? It seems like this is your actual size of the list but I had to check your code to make sure what it is. Call it size or entries or something like this.

---

link *tail;
link *temp;
link *head = NULL;

There is no reason to have temp as a instance variable. And you do not use tail in your code, so drop them both. And use nullptr instead of NULL.

---

void add_node(int data){
 temp = new link;
 temp->data = data;
 temp->next = NULL;
 if (head == NULL){
 head = temp;
 boundaries++;
 }
 else{
 link *tail = head;
 while (tail->next != NULL){
 tail = tail->next;
 }
 tail->next = temp;
 boundaries++;
 }
}

Again, use nullptr. And if you had used your tail you wouldn't need to iterate over the whole list to get to the end.

---

void delete_b(){
 link *end = head;
 link *next_to_end = NULL;
 while (end->next != NULL){
 next_to_end = end;
 end = end->next;
 }
 next_to_end->next = NULL;
 end = NULL;
 boundaries--;
}

What's b? (Oh yeah, I think I don't need to remind you about nullptr again.)

---

void add_front(int data){
 link *ptr = new link;
 ptr->next = head;
 ptr->data = data;
 head = ptr;
 boundaries++;
}

add_node and add_front? What's the difference? Sure, I know what the difference is; I've seen the code. However, I don't like to look through the code to see what a function does. Call them add_front and add_back or something like this (head and tail might fit better, programmers will understand).

---

void delete_front(){
 link *new_head = head;
 new_head = head->next;
 head = NULL;
 head = new_head;
 boundaries--;
}

What is this playing around? That's three useless lines of code:

void delete_front(){
 link* tmp = head;
 head = head->next;
 delete tmp;
 boundaries--;
}

---

void add_by_position(int data, int pos){
 link *node = new link;
 link *linker = head;
 node->data = data;
 for (int i = 0; i < pos; i++){
 linker = linker->next;
 }
 node->next = linker;
 linker = head;
 for (int i = 0; i < pos - 1; i++){
 linker = linker->next;
 }
 linker->next = node;
 boundaries++;
}

by_position sounds silly. Call it add_at. And why do you reset linker and start over again? That's totally unnecessary.

void add_at(int data, int pos){
 link *node = new link;
 node->data = data;
 boundaries++;
 if(pos == 0) {
 node->next = head;
 head = node;
 return;
 }
 link *linker = head;
 for (int i = 0; i < pos - 1; i++){
 linker = linker->next;
 }
 node->next = linker->next;
 linker->next = node;
}

---

You should also delete the nodes in your delete/remove functions.

That's everything for now. You could've easily made a template out of this class, however, you should first fix your problems and then - if you like - ask another question with your new code.