m = 3;调用 a = a + f(0); f(0) = 0;a = a + f(1); f(1) = 1;a = a + f(2); f(2) = 1;a = a + f(3); f(3) = 1;
原因在于 两个 int相除,结果仍然是 int,然后再赋值给一个 double变量