课堂

def jiami(txt):
    pass
def jiemi(txt):
    pass
while 1:    #重复执行
    mode = input("退出按0，加密按1，解密按2:")
    if mode=='0':
        print("再见")
        break
    elif mode=='1':
        txt = input("请输入加密内容:")
        s = jiami(txt)
        print("输出结果:",s)
    elif mode=='2':
        txt = input("请输入解密内容:")
        s = jiemi(txt)
        print("输出结果:",s)
    else:
        continue