Two Questions about c++ lambda functions. [Must Read]

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So today i was learning about c++ lambda functions. and i have some doubts.↵
↵
Q.1) See this↵
↵
<spoiler summary="why the output is 2?">↵
         ↵
~~~~~↵
        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.↵
~~~~~↵
↵
↵
</spoiler>↵
↵
Q.2) another question↵
↵
<spoiler summary="~~Spoiler~~This is giving me runtime error why?">↵
↵
~~~~~↵
        function<int(int)> ~~sum = [&](int a)~~get2;↵
        {↵
            // some code↵
            cout << get(2); // how can i use the get function?↵
            return something;↵
        }cout << get2(3);↵
↵
        ~~function<int(int)>~~ get2 = [&](int va)↵
        {↵
            ~~int b = sum(3);↵~~
            return va;↵
        };↵
↵
↵
~~~~~↵
↵
↵
</spoiler>↵
↵
tell me