while语法,while循环又称为条件循环

while 条件:

code1

code2

code3

....

user_db='egon'

pwd_db='123'

while True:

inp_user=input('username>>: ')

inp_pwd=input('password>>: ')

if inp_user == user_db and inp_pwd == pwd_db:

print('login successfull')

else:

print('user or password error')

2 while+break:break的意思是终止掉当前层的循环,.执行其他代码

while True:

print('1')

print('2')

break

print('3')

user_db='egon'

pwd_db='123'

while True:

inp_user=input('username>>: ')

inp_pwd=input('password>>: ')

if inp_user == user_db and inp_pwd == pwd_db:

print('login successfull')

break

else:

print('user or password error')

print('其他代码')

3 while+continue:continue的意思是终止掉本次循环,.直接进入下一次循环

ps:记住continue一定不要加到循环体最后一步执行的代码

n=1

while n <= 10:

if n == 8:

n += 1 #n=9

continue

print(n)

n+=1 #n=11

while True:

if 条件1:

code1

code2

code3

continue #无意义

elif 条件1:

code1

continue #有意义

code2

code3

elif 条件1:

code1

code2

code3

continue #无意义

....

else:

code1

code2

code3

continue #无意义

while循环嵌套

user_db='egon'

pwd_db='123'

while True:

inp_user=input('username>>: ')

inp_pwd=input('password>>: ')

if inp_user == user_db and inp_pwd == pwd_db:

print('login successfull')

while True:

cmd=input('请输入你要执行的命令: ')

if cmd == 'q':

break

print('%s 功能执行...' %cmd)

break

else:

print('user or password error')

print('end....')

while+tag

user_db='egon'

pwd_db='123'

tag=True

while tag:

inp_user=input('username>>: ')

inp_pwd=input('password>>: ')

if inp_user == user_db and inp_pwd == pwd_db:

print('login successfull')

while tag:

cmd=input('请输入你要执行的命令: ')

if cmd == 'q':

tag=False

else:

print('%s 功能执行...' %cmd)

else:

print('user or password error')

print('end....')

while+else (***)

n=1

while n < 5:

if n == 3:

break

print(n)

n+=1

else:

print('在整个循环结束后,会进行判断:只有while循环在没有被break结束掉的情况下才会执行else中的代码')