各个循环区别

for循环：有理智，能提前知道循环会运行多少次

while循环：没头脑，能无限循环（奇异博士：“多玛姆，我来谈判了。”）

if循环：一根筋，只会循环一次

实操项目：

command = ""
while True:
    command = input(">")
if command == "start":
print("THe card has been started")
elif command == "stop":
print("the car has been stopped")
elif command == "help":
print("""
start: make your car start    
stop:make your car stop
quit: to exit
        """)
elif command == "quit":
break
    else:
print("sorry I don't understand")