控制流程之while循环

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')