一道实验题，太难了，做不出来，望高手解答

#include <iostream>
#include <fstream>
using namespace std;

class AbsCollection{
protected:
    int *iPtr;       //指向数组的指针
    int last;        //数组最后一个元素的位置
    int Max_Size;    //数组长度
public:
    AbsCollection(){};
    AbsCollection(int size)
    {
        Max_Size=size;
        iPtr=new int[Max_Size];
        last=-1;
    };
    virtual ~AbsCollection(){}
    void OutSet()
    {
        if(last<0)
        {
            cout<<"Empty set!"<<endl;
            return;
        }
        cout<<"The number of elements:"    <<last+1<<endl;
        for(int *ip=iPtr;ip<=iPtr+last;)
            cout<<*ip++<<" ";
        cout<<endl;
    }
    int getlast() const {return last;}
    int getitem(int i) const {return iPtr[i];}
};

class Set : public AbsCollection
{
public:
    Set():AbsCollection(100){}
    Set(const char *, int);        
    ~Set();                     
    Set operator = (const Set &s);
    void input(int x);              //增加一个元素
    void erase(int x);         //删除一个元素成员函数
    bool isInSet(int x);     //编写判别元素是否属于集合的成员函数
    void intersection(Set &s);  //求两个集合交的函数成员
    void sub(Set &s);         //求两个集合差的成员函数
    void sort();         //编写集合排序的成员函数    
};

Set::Set(const char * file, int maxsize):AbsCollection(maxsize)
{
    ifstream infile(file);
    int i = 0;
    while (infile)
    {
        infile >> iPtr[i];
        i++;
    }
    last = i - 1;
}

Set::~Set()
{
    ofstream outfile("out.txt");
    if (last > 0)
    {
        for (int i = 0; i <= last; i++)
        {
            outfile << iPtr[i] << " ";
        }
        outfile << endl;
    }

    delete [] iPtr;
}

Set Set::operator = (const Set &s)
{
    if (s.getlast() != -1)
    {
        for (int i = 0; i < s.getlast(); ++i)
        {
            this->iPtr[i] = s.iPtr[i];
        }
    }
    return *this;
}


void Set::input(int x)
{
    if (last + 1 > Max_Size)
    {
        cout << "超出最大范围" << endl;
    }
    else
    {
        for (int i = 0; i < last; i++)
        {
            if (x == iPtr[i])
            {
                cout << "有相同元素，插入失败" << endl;
                return;
            }
        }
        iPtr[i] = x;
        last++;
    }
}

void Set::erase(int x)
{
    int flag = 0;
    for (int i = 0; i < last; i++)
    {
        if (x == iPtr[i])
        {
            for (int j = i; j < last; ++j)
            {
                iPtr[j] = iPtr[j + 1];
            }
            iPtr[j] = 0;
            --last;
            flag = 1;
            break;
        }
    }
    if (!flag)
    {
        cout << "没有这个元素" << endl;
    }    
}

bool Set::isInSet(int x)
{
    for (int i = 0; i < last; ++i)
    {
        if (x == iPtr[i])
        {
            return 1;
        }
    }
    return 0;
}

void Set::intersection(Set &s)
{
    for (int i = 0; i < s.getlast(); i++)
    {
        if (isInSet(s.getitem(i)))
        {
            cout << s.getitem(i) << " ";
        }
    }
}

void Set::sub(Set &s)
{
    for (int i = 0; i < s.getlast(); i++)
    {
        if (isInSet(s.getitem(i)))
        {
            erase(s.getitem(i));
        }
    }
}

void Set::sort()
{
    int flag = 0;
    for (int i = 0; i < last; ++i)
    {
        for (int j = last-1; j > i; --j)
        {
            if (iPtr[j] < iPtr[j - 1])
            {
                iPtr[j] = iPtr[j - 1] + iPtr[j];
                iPtr[j - 1] = iPtr[j] - iPtr[j - 1];
                iPtr[j] = iPtr[j] - iPtr[j - 1];
                flag = 1;
            }            
        }
        if (flag == 0)
        {
            return;
        }
    }
}

Set operator + (Set &s1, Set &s2) //重载+运算符，用于求两个集合的并
{
    Set s;
    for (int i = 0; i < s2.getlast(); ++i)
    {
        if (s1.isInSet(s2.getitem(i)))
        {
            continue;
        }
        else
        {
            s1.input(s2.getitem(i));
        }
    }
    s = s1;
    return s;
}

ostream & operator << (ostream &out, Set &s) //重载<<运算符，用于在屏幕上输出集合元素
{
    if (s.getlast()<0)
    {
        out << "error!";
        return out;
    }
    for (int i = 0; i < s.getlast(); ++i)
    {
        out << s.getitem(i) << " ";
    }
    out << endl;
    return out;
}

int main()
{
    Set sa("in1.txt",100);
    cout << sa;
    return 0;
}