Ah. Yes, I was confused; I thought the issue was the promotion of the 2 from int to floating point.

Also I made an error - should have been

    *(1+a) = 1;

Still bad but not as bad.

After thinking about it a bit, that also is well-typed in C. (You can argue that it shouldn't be allowed, but that's a different argument than that the language is not strongly-typed because of that feature.)

Or:

  1[a] = 1;