Compilation Errors regarding linking h and cpp files

[nadavr]

Hello,

I've received an homework assignment to create an array via linked list.
All went well until the compilation part where i get continuous errors.
Seems most of the problem is that certain classes (DSA_array) doesn't recognize the existence of other classes and their member functions (DSA_list).
Here's my code , hope you can help:

DSA_array.h:

#include "DSA_list.h"
#include <new>
#include <iostream>

using namespace std;
         
DSA_list_node::DSA_list_node(){
                     next = NULL;
                      }
                           
DSA_list::DSA_list(){
                head = NULL; 
                 }
                                 
int DSA_list::get_list_size(){
          DSA_list_node *current = head;
          int counter=0;
          while (current->next != NULL) {
                counter++;
                current = current->next;
                }
          return counter;
          }
     
DSA_list_node* DSA_list::find(DSA_list_node* x){
                     int i;
                     DSA_list_node *current = head;
                     DSA_list_node *answer = NULL;
                     for(i=0; i < this->get_list_size() ; i++) {
                              if (x->data==current->data) { answer = current;}
                              }
                     return answer;  
                     }
                     
DSA_list_node* DSA_list::find_index(int index) {
        DSA_list_node *current = head;
        while(current->next != NULL && current->index != index) {
            current = current->next; }
        return current;
    }
                     
           
bool DSA_list::insert(DSA_list_node* x) {
           if (this->find(x) == NULL) {
                        DSA_list_node *current=head;
                        while(current->next != NULL) {
                                            current = current->next; }
                        current->next = x;
                        return 1; }
           else { return 0;}
           }

DSA_array.cpp:

#include "DSA_list.h"
#include "DSA_array.h"
#include <new>
#include <iostream>

using namespace std;

DSA_array::DSA_array(int size){
                            DSA_list *newlist = new (std::nothrow) DSA_list();
                            int array_size = size;
                           }
                        
DSA_array::~DSA_array(){
        
                  int i;
                  for (i=0; i < array_size; i++) {
                      if (*newlist.find_index(i) != NULL) {
                            delete *newlist.find_index(i);
                               }
                          }
       
int DSA_array::get_assigned_quantity() {
                
                return *newlist.get_list_size();
                
                 }
                       
bool DSA_array::update_array(int x, int y) {
                  if (x > array_size) { return 0; }
                  else {
                        if (*newlist.find_index(x) == NULL) {
                        DSA_list_node *newnode = new (std::nothrow) DSA_list_node();
                        *newnode.data = y;
                        *newnode.index = x;
                        *newlist.insert(*newnode); }
                        else { *newlist.find_index(x).index = y;
                       }
                  return 1; 
                  }
             
void DSA_array::print_array(){
                  int i;
                  for (i=0; i < array_size; i++) {
                      if (*newlist.find_index(i) != NULL) {
                            cout << i << "," << *newlist.find_index(i).data << " "; }
                    }
            }

DSA_list.h:

#ifndef DSA_LIST_H
#define DSA_LIST_H

using namespace std;

class DSA_list_node{
      public:
             int data;
             int index;
             DSA_list_node* next;
             DSA_list_node();
             ~DSA_list_node();
      
      };
      
class DSA_list {
      public:
             DSA_list_node *head;
            
             
             DSA_list();
             ~DSA_list();
             int get_list_size();
             DSA_list_node* find(DSA_list_node *x);
             bool insert(DSA_list_node *x); 
             DSA_list_node* find_index(int index);
      };
      
#endif

DSA_list.cpp:

#include "DSA_list.h"
#include <new>
#include <iostream>

using namespace std;
         
DSA_list_node::DSA_list_node(){
                     next = NULL;
                      }
                           
DSA_list::DSA_list(){
                head = NULL; 
                 }
                                 
int DSA_list::get_list_size(){
          DSA_list_node *current = head;
          int counter=0;
          while (current->next != NULL) {
                counter++;
                current = current->next;
                }
          return counter;
          }
     
DSA_list_node* DSA_list::find(DSA_list_node* x){
                     int i;
                     DSA_list_node *current = head;
                     DSA_list_node *answer = NULL;
                     for(i=0; i < this->get_list_size() ; i++) {
                              if (x->data==current->data) { answer = current;}
                              }
                     return answer;  
                     }
                     
DSA_list_node* DSA_list::find_index(int index) {
        DSA_list_node *current = head;
        while(current->next != NULL && current->index != index) {
            current = current->next; }
        return current;
    }
                     
           
bool DSA_list::insert(DSA_list_node* x) {
           if (this->find(x) == NULL) {
                        DSA_list_node *current=head;
                        while(current->next != NULL) {
                                            current = current->next; }
                        current->next = x;
                        return 1; }
           else { return 0;}
           }

Thank you !

[Fbody]

Why are you implementing the members of DSA_List in both DSA_list.cpp and in DSA_array.h?