I want to implement a function in C++ that returns the set difference between 2

Question

I want to implement a function in C++ that returns the set difference between 2 arrays ,

the set difference is the set of objects in set A - the objects in A intersection B

for example :

if we have set1 = {1,3,5} and set2 = {3,4,5} then the set difference is 1

so i have implemented the setIntersection function properly , but my setDifference function does not work properly here is the code:

// need imporvement on this one ???

int setDifference(int list1[], int list2[], int m, int n) //difference function

{
int i = 0, j = 0;
int *C ;
while(i < m && j < n)
{
if(list1[i]!=list2[i])
{
C[i]= list1[i];
}
}

for(int k=0;k<i;k++) //printing value after (A-B) difference
{
cout<< C[k]<<endl;
}
return *C;
}

// this one works just fine for an ordered array

int setIntersection (int list1[], int list2[], int m, int n)
{
    int i = 0, j = 0;
while(i < m && j < n)
{
if (list1[i] < list2[j])
i++;
else if (list2[j] < list1[i])
j++;

else
{
cout << list2[j++]<<",";
i++;
}
}
}

// this is the driver method

int main()
{
   int list1 [] = {1,2,3,4,5,6};
int list2 [] = {1,3,5};
  
int size1 = sizeof(list1) / sizeof(list1[0]);
int size2 = sizeof(list2) / sizeof(list2[0]);
// call the function here
  

cout << "Union set: " << endl;
setUnion(list1, list2, size1, size2);
  
cout<< " Intersection set: " << endl;
setIntersection(list1, list2, size1, size2);
  
cout<< " Difference set: " << endl;
setDifference(list1, list2, size1, size2);
return 0;
  
setDiff(list1, list2, size1, size2);
}

Explanation / Answer

change your setDiff method with this new setDifference method -----

int *setDifference(int *list1, int *list2, int size1, int size2)
{
   int *intersection=NULL, *temp=NULL, n=0, i=0, j=0;
   try{
       temp=new int[size1];
   }catch(bad_alloc xa){
       cout<<" Dynamic memory allocation failed ";
       exit(0);
   }
   while(i<size1 && j<size2)
   {
       if(list1[i]==list2[j])
       {
           i++,j++;
       }
       else if(list1[i]<list2[j])
       {
           temp[n++]=list1[i++];
       }
       else
       {
           j++;
       }
   }
   while(i<size1)
   {
       temp[n++]=list1[i++];
   }
   try{
       intersection=new int[n];
   }catch(bad_alloc xa){
       cout<<" Dynamic memory allocation failed ";
       exit(1);
   }
   for(j=0;j<n;j++)
   {
       intersection[j]=temp[j];
   }
   delete [] temp,temp=NULL;
   cout<<" Set Difference ";
   for(j=0;j<n;j++)
       cout<<intersection[j]<<endl;
   return intersection;
}

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