二 while循环

Posted 2021-01-21 martin-wang

1. while循环：条件循环
 I: 基本语法
 while 条件:
     代码1
     代码2
     代码3
     ...

示范:

name_of_bk = ‘egon‘
pwd_of_bk = ‘123‘

tag = True#定义条件为真
while tag:
    inp_name = input(‘your name>>: ‘)#输入姓名
    inp_pwd = input(‘your password>>: ‘)#输入密码
    if inp_name == name_of_bk and inp_pwd == pwd_of_bk: #判断是否姓名,密码一致
        print(‘login successful‘)
        tag = False#改变条件,终止循环
    else:
        print(‘username or password error‘)

    print(‘other code...‘)

　　

2: while+break:break代表结束本层循环
示范：

while True:
    print(1)
    break
    print(2)
    print(3)

name_of_bk = ‘egon‘
pwd_of_bk = ‘123‘

while True:
    inp_name = input(‘your name>>: ‘)
    inp_pwd = input(‘your password>>: ‘)
    if inp_name == name_of_bk and inp_pwd == pwd_of_bk:
        print(‘login successful‘)
        break
    else:
        print(‘username or password error‘)

    print(‘other code......‘)

3: while + continue: continue代表结束本次循环，直接进入下一次
示范

count=1
while count < 6:
    if count == 3:
        count+=1
        continue
    print(count)
    count+=1

4:while + else

else的子代块只有在while循环没有被break打断的情况下才会执行

 count=0
 while True:
     if count == 10:
         break
     print(count)
     count+=1

 else:
     print("")
  

注意:

两个经典代码:

简单购物车

简单的购物程序:
name_of_bk=‘egon‘
pwd_of_bk=‘123‘

count=0
tag=True
while tag:
    if count == 3:
        print(‘输错的次数过多。。。‘)
        break
    inp_name=input(‘your name>>: ‘)
    inp_pwd=input(‘your password>>: ‘)
    if inp_name == name_of_bk and inp_pwd == pwd_of_bk:
        print(‘login successful‘)
        while tag:
            print("""
            0 退出
            1 购物
            2 支付
            3 查看购物
            """)
            cmd=input(‘>>>: ‘)
            if cmd == ‘0‘:
                tag=False
                continue
            if cmd == ‘1‘:
                print(‘购物。。。。。。。‘)
            elif cmd == ‘2‘:
                print(‘支付。。。。。‘)
            elif cmd == ‘3‘:
                print(‘查看购物车‘)
            else:
                print(‘输入错误的指令‘)
    else:
        print(‘username or password error‘)
        count+=1 #count=3 输错3次

View Code

 

输错三次退出　

 1 输错三次退出
 2  name_of_bk = ‘egon‘
 3  pwd_of_bk = ‘123‘
 4 
 5  count = 0
 6  while True:
 7      if count == 3:
 8          print(‘输错的次数过多。。。‘)
 9          break
10      inp_name = input(‘your name>>: ‘)
11      inp_pwd = input(‘your password>>: ‘)
12      if inp_name == name_of_bk and inp_pwd == pwd_of_bk:
13          print(‘login successful‘)
14          break
15      else:
16          print(‘username or password error‘)
17          count += 1  # count=3 输错3次

View Code

句型:循环嵌套

　tag=True 

　　while tag:

　　　　......

　　　　while tag:

　　　　　　........

　　　　　　while tag:

　　　　　　　　tag=False