[mikeash]

It is quite confusing, because it implies that this is equivalent and equivalently wouldn't work:

    int *ptr = &x;
    ptr = 20;

The rvalue/lvalue distinction is completely unrelated to pointers, holding memory addresses versus numbers representing memory addresses, etc. The & operator simply doesn't give you an lvalue, like most operators in C, and this has nothing to do with addresses, pointers, or anything of the like

[denniskubes]

After rereading it a couple times I think you and others were right. I was trying to say something that in the end muddied issue. I have removed the section on r-value and l-values.