(七) 流程控制之while循环
条件循环:while,语法如下
while 条件: (又称为条件循环)
# 循环体
# 如果条件为真,那么循环体则执行,执行完毕后再次循环,重新判断条件。。。
# 如果条件为假,那么循环体不执行,循环终止
while+break
while+break:break的意思是结束本层循环
while True:
name=input('please input your name: ')
pwd=input('please input your password: ')
if name == 'egon' and pwd == '123':
print('登录成功')
break
else:
print('用户名或密码错误')
while+continue
while+continue:continue的意思是结束本次循环,进入下一次循环
n=1
while n <= 5:
if n == 4: #n =4
n+=1 # n=5
continue
print(n)
n+=1
打印0-10
count=0
while count<=10:
print(count)
count=count+1
打印偶数
count=0
while count <=10:
if count%2==0:
print(count)
count=count+1
==3 死循环
import time
num=0
while True:
print('count',num)
time.sleep(1)
num+=1 ==
循环嵌套与tag
tag=True
while tag:
......
while tag:
........
while tag:
tag=False
练习,要求如下:
1 循环验证用户输入的用户名与密码
2 认证通过后,运行用户重复执行命令
3 当用户输入命令为quit时,则退出整个程序
name="bruce"
password="123"
while True:
inp_name=input('username>>>')
inp_pswd=input('password>>>')
if inp_name==name and inp_pswd==password:
while True:
cmd=input('>>>:')
if not cmd:continue
if cmd=="quit":
break
print("run <%s>" %cmd )
else:
print("incorrect username or password")
continue
break
为什么
if not cmd:continue
if cmd=="quit"
不能把if not 放下面, 为什么有冒号而不是等号
*while+else*与其它语言else 一般只与if 搭配不同, 在Python 中还有个while ...else 语句, while 后面的else 作用是指当while 循环正常执行完,中间没有被break 中止的话,就会执行else后面的语句
number_1=0
while number_1<=5:
number_1 += 1
if number_1==3:
break
print(number_1)
else:print('finished')
1
2
#1. 使用while循环输出1 2 3 4 5 6 8 9 10
count_1=1
while count_1 <= 10:
if count_1 == 7:
count_1 += 1
continue
print(count_1)
count_1+=1
count_2=1
while count_2<=10:
if count_2!=7:
print(count_2)
count_2+=1
求1-100的所有数的和
plus_1=0
plus_2=plus_1+1
while plus_1<=100:
plus_2=plus_1+plus_2
plus_1+=1
print(plus_2)
求1-2+3-4+5...99的值
res=0
count_4=1
while count_4<=100:
if count_4%2==0:
res=res-count_4
else:
res=res+count_4
count_4+=1
print(res)
. 用户登陆(三次机会重试)
retry=3
u_='bruce'
p_='123'
while retry :
username_= input('input your username>>: ')
password_=input('input your password>>>: ')
if username_==u_ and password_==p_:
print("login success")
break
else:
retry -= 1
print('login failed, {} times left' .format (retry))