C++ Union , Intersection , Difference - c++

Question

So I'm working on a code to find the Union, Intersection and Difference between two arrays. I'm done with the Union and Intersection but i just can't figure out the difference(A - B) ,For example A={1,3,6,9,7,9} , B={2,3,-2,9} i want to get A - B = { 1,6,7,0} .
I don't want to use any other library except iostream.
This is my code so far.
/* Prints union of A[] and B[]
SizeA is the number of elements in A[]
SizeB is the number of elements in B[] */
cout << "\nUnion of A and B = "; //
i = 0; j = 0;
while (i < SizeA && j < SizeB)
{
if (A[i] < B[j])
cout << A[i++] << " ";
else if (B[j] < A[i])
cout << B[j++] << " ";
else
{
cout << B[j++] << " ";
i++;
}
}
/* Print remaining elements of the larger array */
while (i < SizeA)
cout << A[i++] << " ";
while (j < SizeB)
cout << B[j++] << " ";
cout << "\nIntersection of A and B = ";
for (i = 0; i < SizeA; i++) //for loop to calculate the intersection of A and B.
{
for (j = 0; j < SizeB; j++)
{
if (A[i] == B[j])
{
cout << A[i] << " ";
}
}
}

Answer 1

This is very bad practice because it's not general, not using a clean function and using plain old arrays but I assumed that you are beginner and have to do it in this way
#include <iostream>
int main()
{
int A [] ={1,3,6,9,7}, Asz = 5, B [] ={2,3,-2,9}, Bsz = 4;
std::cout << "\nThe difference is {";
for( int i = 0; i < Asz; ++i){
int temp = A[i];
bool notFound = true;
for(int j = 0; j < Bsz; ++j){
if(temp == B[j]) notFound = false;
}
if(notFound)
{
if(i < Asz - 1) std::cout << temp << ", ";
else std::cout << temp ;
}
}
std::cout << "}";
}
The way I prefer
#include <iostream>
#include <vector>
#include <algorithm>
int main()
{
std::vector<int> A = {1,3,6,9,7, 0} , B={2,3,-2,9}, C;
std::sort(A.begin(), A.end());
std::sort(B.begin(), B.end());
std::set_difference(A.cbegin(), A.cend(), B.cbegin(), B.cend(), std::back_inserter(C), std::less<int>{});
for(auto const & el : C)
std::cout << el << ", ";
}

Answer 2

If you could save the intersection, you could then just check each element of A and B against the elements of the intersection. Otherwise, you need two for-loops:
cout << "\nDifference of A and B = ";
for (i = 0; i < SizeA; i++) //for loop to calculate the intersection of A and B.
{
bool found = false
for (j = 0; j < SizeB; j++)
{
if (A[i] == B[j])
{
found = true;
}
}
if (!found) {
cout<<A[i]<<" ";
}
}
for (i = 0; i < SizeB; i++)
{
bool found = false
for (j = 0; j < SizeA; j++)
{
if (B[i] == A[j])
{
found = true;
}
}
if (!found) {
cout<<B[i]<<" ";
}
}
Edit: Never mind, i got the definition of difference wrong (thought it was (A-B) + (B-A)), so only the first for-loop is needed, and there's no point saving the intersection.