Question

HOW DO I ACCESS THE HEAD OF A LINKED LIST FROM INT MAIN () WHEN IT'S IN ANOTHER CLASS. HERE IS MY CODE FOR MY MAIN AND HEADER FILES.

HEADER FILE:

#ifndef HANOISTACK_H
#define HANOISTACK_H
#include <iostream>
using namespace std;

class HanoiStack { //class
private:
struct Disc{ //linked list for towers
int num;
Disc* next;
};
Disc* head;

public:
HanoiStack(){ //constructor
head = nullptr;
};
//HanoiStack operator+=(const Disc&);
//HanoiStack operator<<(const Disc&);
void push(int); //push function
int pop(); //pop function
void display(int);//prints pegs
};
#endif

MAIN FILE

int main(){
//class objects
HanoiStack peg;
HanoiStack temp1;
HanoiStack temp2;
HanoiStack temp3;
//integer variables

int num, solved, choice, end, removed, count = 0, tower;
//win condition variable
bool won = false;

cout << "Enter the number of disks" << endl;
cin >> num;//enters the number of disks
while (num > 0 && num < 10){ //confirmation loop
cout << "Error wrong entry try again" << endl;
cout << "Enter the number of disks" << endl;
cin >> num;
}
if (num > 0 && num < 10){
solved = pow(2, num)-1; //minimum number of moves required to win
}

for (int i = num; i > 0; i--){
peg.push(temp1); //inserts disks onto tower
}

Answer 1

You need to change the visibility of head from private to public to be able to access it outside the class but that would be a violation of Object-Oriented Programming paradigm. You can modify your class as:

#ifndef HANOISTACK_H
#define HANOISTACK_H
#include <iostream>
using namespace std;

class HanoiStack { //class
private:
    struct Disc{ //linked list for towers
        int num;
        Disc* next;
    };

public:
    Disc* head;
    
    HanoiStack(){ //constructor
        head = nullptr;
    };
    //HanoiStack operator+=(const Disc&);
    //HanoiStack operator<<(const Disc&);
    void push(int); //push function
    int pop(); //pop function
    void display(int);//prints pegs

};
#endif

Now, you can access head of the linked list as:

HanoiStack temp1;
cout << temp.head->num << endl; // to print num at head of the list

Avoid this design though. Another approach could be, bring your struct Disc definition out of the class and keep head of the list private in the class. Now, make a member function of the class Disc* getHead() which would return the head of the linked list. Do changes as follow:

#ifndef HANOISTACK_H
#define HANOISTACK_H
#include <iostream>
using namespace std;

struct Disc{ //linked list for towers
    int num;
    Disc* next;
};

class HanoiStack { //class
private:
    Disc* head;

public:
    HanoiStack(){ //constructor
        head = nullptr;
    };
    Disc* getHead() { return head; }
    
    //HanoiStack operator+=(const Disc&);
    //HanoiStack operator<<(const Disc&);
    void push(int); //push function
    int pop(); //pop function
    void display(int);//prints pegs
};
#endif

Now, to access the head of the linked list you could do:

HanoiStack temp1;
Disc *temp1head = temp1.getHead(); // this will return head of the linked list of temp1
cout << temp1head->num << endl; // to access number at the head

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