accessing variables from an intended block of nested blocks [duplicate]

Answer 1

Use references.

// Block A
int aa = 30;
auto& ref_aa = aa;
{
    // Block B
    int aa = 40;

    {
        // Block C
        int aa = 50;

        cout << "block C " << aa << endl;
        cout << "block A " << ref_aa << endl;
        cout << "global" << ::aa << endl;
    }

    cout << "block B " << aa << endl;
}

Of course, that's quite meaningless; if you can modify the code, then just change the variable names, or refactor it such that fewer blocks are needed (using more functions, for example).

Answer 2

I know that this is not good code. Just curious in understanding how to achieve it.

You can't.

Undecorated use of the variable aa will use the one that is in the nearest scope.
Decorated use of the variable, ::aa, will use the one that is in the scope outside the function.
Decorated use of the variable, <NS>::aa, will use the one that is in the scope of the namespace <NS>.