From http://eli.thegreenplace.net/2011/05/02/the-context-sensitivity-of-c%E2%80%99s-grammar-revisited/

gistfile1.c

typedef int AA;

void foo()
{
  AA AA;            /* OK - define variable AA of type AA */
  int BB = AA * 2;  /* OK - AA is just a variable name here */
}