A.switch(a+b) { case 1: printf("* "); 　case 2+1: printf("** "); }
B.switch((int)x); { case 1: printf(" * n "); case 2: printf(" ** n "); }
C.switch(x) { case 1.0: printf(" * n "); case 2.0: printf(" ** n "); }
D.switch(a+b) { case 1: printf(" * n "); case c: printf(" ** n "); }