You inspired me this joyful rewrite:

    #define _(e) { e;};
    #define r(e) _(return e)
    #define I(b, e) _(if (b) r(e));
    #define W(e) _(while (1) _(e));
    int main(int c, char **v) {
      _(I(c != 2, -1) _(c = 0) W(I(!v[1][c++], v[1][c - 2] & 1)))
    }