C++ Changing Struct to Class [closed] - c++

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I am doing linked list exercises and currently understand how to write a link list in struct format. However I would like to change my code to make linked list a class and have the print, sort, add, delete, functions as members of the class. Please give me ideas on how this can be done.
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <cstddef>
using namespace std;
struct mylist {
int payload;
struct mylist * link;
};
void addlink(struct mylist *, int);
struct mylist * droplink(struct mylist *);
void printmylist(struct mylist *);
void sortmylist(struct mylist *);
int main() {
struct mylist head;
struct mylist *lptr;
head.payload = 15;
head.link = 0;
lptr = &head;
printmylist(lptr);
addlink(lptr, 21);
printmylist(lptr);
addlink(lptr, -5);
printmylist(lptr);
addlink(lptr, 90);
printmylist(lptr);
lptr = droplink(lptr);
printmylist(lptr);
sortmylist(lptr);
printmylist(lptr);
return 0;
}
void addlink(struct mylist *lp, int val) {
struct mylist *temp;
struct mylist *newlink;
//run out to end of chain
temp = lp;
do {
if (temp->link != 0)
temp = temp->link;
} while (temp->link != 0);
newlink = (struct mylist *) malloc(sizeof(struct mylist));
newlink->payload = val;
newlink->link = 0;
temp->link = newlink;
return;
}
struct mylist * droplink(struct mylist *lp) {
cout << "Releasing front value of " << lp->payload << endl;
return lp->link;
}
void printmylist(struct mylist *lp) {
struct mylist *temp;
temp = lp;
while (temp->link != 0) {
cout << temp->payload << " then ";//if there is just one link, loop never runs
if (temp->link != 0)
temp = temp->link;
}
cout << temp->payload; //gets the last link's value
cout << endl;
return;
}
void sortmylist(struct mylist *lp) {
struct mylist *temp;
struct mylist *temp2;
int linkcount = 1;
int temppayload;
temp = lp;
while (temp->link != 0) {
if (temp->link != 0) {
++linkcount;
temp = temp->link;
}
}
cout << linkcount << " links " << endl;
temp = lp;
for (int ct2 = 1; ct2 < linkcount; ++ct2) {
temp = lp;
for (int ct = 1; ct < linkcount; ++ct) {
if (temp->link != 0)
temp2 = temp->link;
if (temp->payload > temp2->payload) {
temppayload = temp->payload;
temp->payload = temp2->payload;
temp2->payload = temppayload;
}
if (temp2->link != 0)
temp = temp2;
}
}
}

Answer 1

The only real difference between a struct and a class in C++ is that by default all members of a class are private, and all members of a struct are public.
I assume what you're really asking is how to make your linked list methods members of your struct / class. This is very easy.
All of your existing methods accept a struct mylist* as the first parameter. In C++, this is provided automatically by the compiler, as a hidden parameter called this. You can refer to this explicitly, but it is also accessible implicitly.
So where in C you might have:
lp->payload = 0;
In a C++ class member function, you could have:
this->payload = 0;
Or more commonly:
payload = 0;
So broadly speaking, the steps required to "c++ify" your C code are:
Move the declarations of the methods into the body of the struct
Remove the struct mylist * argument from each method
Remove the references to lp in each method
Call the member functions by dereferencing an instance of the struct (e.g. lptr->addlink(-5);)

Answer 2

As a rule, you can change every struct that is passed to a linked list function from:
struct Node {
int payload;
struct Node *link;
};
...
void addlink(struct Node *lp, int val) {
...
}
to this:
class Node {
public:
Node() : _link(0), _payload(0) { } // initialize members on new empty node
Node(int val) : _link(0), _payload(val) { } // pass a new value directly
~Node() {
// call a function to clear everything pointed to from _link
}
void addlink(int val) {
Node *temp = this;
do {
if (temp->link() != 0)
temp = temp->link();
} while (temp->link() != 0);
Node *newlink = new Node(val); // this will do what the next 2 lines do
//Node *newlink = new Node; <- you can also create a Node this way and then assign the payload
//newlink->setPayload(val);
// newlink->link = 0; <-- not needed 'new Node' has already initialized it
temp->setLink(newlink);
}
// provide access to the data (get/set)
int payload() { return _payload; }
void setPayload(int n) { _payload = n; }
Node *link() { return _link; }
void setLink(Node *p) { _link = p; }
// data members
private:
int _payload;
Node *_link;
};
This fragment gives you the idea. Now you can add the rest :)
The best of course, is to place the code within the functions in a .cpp file and leave the definition of the class in the header:
class Node {
public:
Node();
Node(int val); // pass a new value directly
~Node();
void addlink(int val);
// provide access to the data (get/set)
// you can leave thse one liners in the header, they'll most likely be inlined
int payload() { return _payload; }
void setPayload(int n) { _payload = n; }
Node *link() { return _link; }
void setLink(Node *p) { _link = p; }
// data members
private:
int _payload;
Node *_link;
};
The bodies of the functions in the cpp:
Node::Node() : _link(0), _payload(0)
{
}
Node::Node(int val) : _link(0), _payload(val)
{
}
......
Hope this helps.