改造Set类，重载+（并集）、（-）差集、*（交集）、<<（输出）、>>（输入）和函数调用操作符（添加一个元素）

以下是改造后的Set类的代码，包括重载的操作符和函数：

#include <iostream>
#include <set>

using namespace std;

class Set
{
private:
    set<int> s;

public:
    Set() {}

    Set(initializer_list<int> l)
    {
        for (auto i : l)
        {
            s.insert(i);
        }
    }

    Set operator+(const Set &other) const
    {
        Set result;
        set_union(s.begin(), s.end(), other.s.begin(), other.s.end(), inserter(result.s, result.s.begin()));
        return result;
    }

    Set operator-(const Set &other) const
    {
        Set result;
        set_difference(s.begin(), s.end(), other.s.begin(), other.s.end(), inserter(result.s, result.s.begin()));
        return result;
    }

    Set operator*(const Set &other) const
    {
        Set result;
        set_intersection(s.begin(), s.end(), other.s.begin(), other.s.end(), inserter(result.s, result.s.begin()));
        return result;
    }

    friend ostream &operator<<(ostream &out, const Set &set)
    {
        out << "{ ";
        for (auto i : set.s)
        {
            out << i << " ";
        }
        out << "}";
        return out;
    }

    friend istream &operator>>(istream &in, Set &set)
    {
        int num;
        cout << "Enter element (-1 to stop): ";
        while (true)
        {
            in >> num;
            if (num == -1)
            {
                break;
            }
            set.s.insert(num);
            cout << "Enter element (-1 to stop): ";
        }
        return in;
    }

    void operator()(int num)
    {
        s.insert(num);
    }
};

使用示例：

int main()
{
    Set a = {1, 2, 3, 4};
    Set b = {3, 4, 5, 6};

    Set c = a + b;
    Set d = a - b;
    Set e = a * b;

    cout << "a: " << a << endl;
    cout << "b: " << b << endl;
    cout << "a + b: " << c << endl;
    cout << "a - b: " << d << endl;
    cout << "a * b: " << e << endl;

    Set f;
    cin >> f;
    cout << "f: " << f << endl;

    f(10);
    cout << "f: " << f << endl;

    return 0;
}

输出结果：

a: { 1 2 3 4 }
b: { 3 4 5 6 }
a + b: { 1 2 3 4 5 6 }
a - b: { 1 2 }
a * b: { 3 4 }
Enter element (-1 to stop): 7
Enter element (-1 to stop): 8
Enter element (-1 to stop): -1
f: { 7 8 }
f: { 7 8 10 }