2018.09.14python學習第四天part2

流程控制之while循環

1.什么是循環？（what）

循環是指重復做某一件事

2.為何要有循環？（why）

為了讓計算機能像人一樣重復去做某一件事

3.如何使用循環？（how）

#語法一：while條件

如：用戶登錄時信息輸入錯誤是需要重新輸入

name_bd="tony"
pwd_bd=123
while True:name=input("please your name: ")pwd=input("plesse your password: ")if name == name_bd and pwd == pwd_bd:print("login successful")else:print("please input again")

輸入這段代碼后，會發現無論你登錄是否成功，都是無限循環登錄，所以要讓登錄成功后就結束循環應該：

name_bd="tony"
pwd_bd="123"
a=True
while a:name=input("please your name: ")pwd=input("please your password: ")if name == name_bd and pwd == pwd_bd:print("login successful")a=Falseelse:print("please input again")

#語法二：while+break（break表示強制結束本層循環）

name_bd="tony"
pwd_bd="123"
while True:name=input("please your name: ")pwd=input("plesse your password: ")if name == name_bd and pwd == pwd_bd:print("login successful")breakelse:print("please input again")

這樣也實現了登陸成功是終止循環

#語法三：while+continue（continue表示停止本次循環，直接進入下一次）

count=0
while count<10:if count ==5:count+=1continueprint(count)count+=1

#語法四：while+else（else會在while循環沒有被break終止的情況下執行）

name_bd="tony"
pwd_bd="123"
count=0
while count<=2:        name=input("please your name: ")pwd=input("plesse your password: ")if name == name_bd and pwd == pwd_bd:print("login successful")breakelse:print("please input again")count+=1
else:print("輸錯次數太多，請稍后"）

#語法五：while循環的嵌套

name_bd="tony"
pwd_bd="123"
count=0while count<=2:name=input("please your name: ")pwd=input("plesse your password: ")if name == name_bd and pwd == pwd_bd:print("login successful")while True:print("1.瀏覽商品，2.添加購物車，3.支付，4.退出")choice=input("請輸入你的選擇： ")if choice=="1":print("正在瀏覽商品")if choice=="2":print("正在添加購物車")if choice=="3":print("正在支付")if choice=="4":breakbreakelse:print("please input again")count+=1
else:print("輸錯次數太多，請稍后")

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