DSA set operations

#include <iostream>
#include <cstdlib>
using namespace std;
class node
{
public:
string name;
node *next;
};
node *temp1;
class Set
{
node *head, *last, *temp;
public:
void add();
Set union_list(Set);
Set intersection_list(Set);
void display();
bool isPresent(Set, string);
Set()
{
head = last = temp = NULL;
}
};
void Set::display()
{
temp = head;
while(temp!=NULL)
{
cout<<temp->name<<"    ";
temp = temp->next;
}
}
void Set::add()
{
temp = new node;
cout<<"\nEnter name: ";
cin>>temp->name;
temp->next = NULL;
if(head == NULL)
head = last = temp;
else
{
last->next = temp;
last = temp;
}
}
bool Set::isPresent(Set X, string str)
{
temp = X.head;
while(temp != NULL)
{
if(temp->name == str)
return true;
temp = temp->next;
}
return false;
}
Set Set::union_list(Set C)
{
Set X;
node *temp1 = head, *temp2 = C.head;
while(temp1 != NULL)
{
temp = new node;
temp->name = temp1->name;
temp->next = NULL;
if(X.head == NULL)
X.head = X.last = temp;
else
{
X.last->next = temp;
X.last = temp;
}
temp1 = temp1->next;
}
while(temp2 != NULL)
{
if(!isPresent(X, temp2->name))
{
temp = new node;
temp->name = temp2->name;
temp->next = NULL;
if(X.head == NULL)
X.head = X.last = temp;
else
{
X.last->next = temp;
X.last = temp;
}
}
temp2 = temp2->next;
}
return X;
}
Set Set::intersection_list(Set C)
{
Set X;
node *temp1 = head;
while(temp1 != NULL)
{
if(isPresent(C, temp1->name))
{
temp = new node;
temp->name = temp1->name;
temp->next = NULL;
if(X.head == NULL)
X.head = X.last = temp;
else
{
X.last->next = temp;
X.last = temp;
}
}
temp1 = temp1->next;
}
return X;
};
int main()
{
int ch;
Set V, B, U, I, T;
while(1)
{
cout<<"\n\n1. Enter name of students who like vanilla ice-cream.";
cout<<"\n2. Enter name of students who like butter-scotch ice-cream.";
cout<<"\n3. Display list of students who like vanilla. ";
cout<<"\n4. Display list of students who like ice-cream.";
cout<<"\n5. Display union. ";
cout<<"\n6. Display intersection";
cout<<"\n7. Exit";
cout<<"\nEnter your choice: ";
cin>>ch;
switch(ch)
{
case 1: V.add(); break;
case 2: B.add(); break;
case 3: cout<<"\nStudents who like vanilla: "<<endl;
V.display(); break;
case 4: cout<<"\nStudents who like butter-scotch: "<<endl;
B.display(); break;
case 5: cout<<"\nStudents who like vanilla: "<<endl;
V.display();
cout<<"\nStudents who like butter-scotch: "<<endl;
B.display();
cout<<"\nUnion: "<<endl;
U = V.union_list(B); U.display(); break;
case 6: cout<<"\nStudents who like vanilla: "<<endl;
V.display();
cout<<"\nStudents who like butter-scotch: "<<endl;
B.display();
cout<<"\nIntersection: "<<endl;
I = V.intersection_list(B); I.display(); break;
case 7: exit(0); break;
default: cout<<"\nInvalid choice"; break;
}
}
return 0;
}