以下程序的运行结果是 int x1 = 30, x2 = 40;void sub(int x, int y){ x1 = x; x = y; y = x1; }main(){ int x3 = 10, x4 = 20; sub(x3, x4); sub(x2, x1); printf("%d,%d,%d,%d", x3, x4, x1, x2);}