function<int(int,int)> sum = [&](int a, int b)
        {
            ++a;
            return a+b;
        };
        int a = 2, b = 3;
        int s = sum(a, b);
        cout << a << endl;// why it's 2 i have passed 'a' with refrence. how to pass it with refrence.

        function<void(int)> sum = [&](int a)
        {
            // some code
            cout << get(2); // how can i use the get function?
        };

        function<int(int)> get = [&](int v)
        {
            int b = sum(3);
            return v;
        };