2018.09.14python学习第四天part2

流程控制之while循环

1.什么是循环？（what）

循环是指重复做某一件事

2.为何要有循环？（why）

为了让计算机能像人一样重复去做某一件事

3.如何使用循环？（how）

#语法一：while条件

如：用户登录时信息输入错误是需要重新输入

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")

输入这段代码后，会发现无论你登录是否成功，都是无限循环登录，所以要让登录成功后就结束循环应该：

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")

#语法二：while+break（break表示强制结束本层循环）

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")

这样也实现了登陆成功是终止循环

#语法三：while+continue（continue表示停止本次循环，直接进入下一次）

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

#语法四：while+else（else会在while循环没有被break终止的情况下执行）

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("输错次数太多，请稍后"）

#语法五：while循环的嵌套

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.浏览商品，2.添加购物车，3.支付，4.退出")choice=input("请输入你的选择： ")if choice=="1":print("正在浏览商品")if choice=="2":print("正在添加购物车")if choice=="3":print("正在支付")if choice=="4":breakbreakelse:print("please input again")count+=1
else:print("输错次数太多，请稍后")