intersection of sets in C++ - c++

Question

i am trying to do simple sets intersection , it works correctly , but when output comes , it shows only memory address or garbage random value , help me ,i applied breakpoints , but it's not working . actually i am new in C++
#include<iostream>
using namespace std;
class set
{
private:
int size;
int *elem;
public:
set()
{
size = 0;
elem = NULL;
}
set(int s);
~set();
set(set &s);
set intersection(set A, int z);
void inputset();
void outputset();
};
set::set(int s)
{
size = s;
elem = new int[s];
}
void set::inputset()
{
int i;
cout << "Enter the set Element" << endl;
for(i = 0 ; i < size ; i++)
{
cin >> elem[i];
}
}
set set::intersection(set A, int z)
{
int i, j, k = 0;
set R(z);
for(i = 0; i < size; i++)
{
for(j = 0; j < A.size; j++)
{
if(elem[i] == A.elem[j])
{
R.elem[k] = A.elem[j];
k++;
break;
}
}
}
return R;
}
set::~set()
{
delete []elem;
}
set::set(set &s)
{
int i;
if(size > 0)
{
delete []elem;
}
size = s.size;
elem = new int[size];
for(i = 0; i < size; i++)
{
elem[i] = s.elem[i];
}
}
void set::outputset()
{
int i;
cout << "The elements of new set is : " << endl;
for(i = 0; i < size; i++)
{
cout << elem[i] << endl;
}
cout << endl;
}
int main()
{
int x, y, z;
char choice;
cout << "Enter sizeof set A" << endl;
cin >> x;
set S1(x);
S1.inputset();
S1.outputset();
cout << "Enter sizeof set B" << endl;
cin >> y;
set S2(y);
S2.inputset();
S2.outputset();
z = x + y;
set S3(z);
cout << "Enter I for intersection" << endl << "Enter U for union" << endl << "Enter D for difference" << endl;
cin >> choice;
switch(choice)
{
case'I':
S3 = S1.intersection(S2, z);
S3.outputset();
break;
default:
cout << "Invalid entry";
}
return 0;
}

Answer 1

There are several ways to check intersections between two sets, if your sets are in arrays, I'd suggest looping one of them and have a check if it's in between the other:
for (int i = 0; i < element1_size; i++) {
for (int u = 0; u < element2_size; u++) {
if (element1[i] == element2[u]) {
cout << "Intersection point : " << element1[i] << endl;
}
}
}

Answer 2

Your copy ctor should be set(const set &s); instead of set(set &s); What you have is a ctor that accepts a reference to set, which is not a copy ctor. So compiler generates default one for you and you have issue returning object by value from method intersection()
Also please fix your code indent, it is not easy to read it.
Also remove following lines from your "copy ctor":
if(size>0)
{
delete []elem;
}
You cannot delete that pointer, your object is not constructed yet.

Answer 3

How about using a map to keep track of the "intersected" elements in much more efficient way. Here is a snippet of what I have in mind:
std::map<int, int> m;
for(int i = 0; i < size; ++i)
m.insert( std::pair<int, int>(elem[i], 1) );
for(int i = 0; i < A.size; ++i)
if(m.count(A[i]) > 0)
R.elem[k++] = A[i]
This way you avoid the nested for-loops, and will be able to compute the intersection with logarithmic time complexity.