根据用户输出的数字输出以下成语

switch(a){case1:b="一帆风顺";break;case2:b="二龙戏珠";break;case3:b="三阳开泰";break;case4:b="四平八稳";break;case5:b="五福临门";break;case6:b="六六大顺";break;case7:b="七星报喜";break