Question

#define NUM_SQ_0 (1 << 1*1)  //<<----- ??

static struct square sq_0[NUM_SQ_0];

Note that square is a struct with 4 pointers to square, defined as follows:

typedef struct square {
    struct square *nw, *ne,
                  *sw, *se;
} *square;

Answer 1

Per C++ operator precedence, the * operator is evaluated first, and that evaluates to the value 1, and then it’s shifted one bit to the left, which is the value 2^1 or just 2.