六、流程控制之while循环

1、什么是循环？

　　循环指的是一个重复做某件事的过程

2、为何要有循环？

　　为了让计算机像人一样能循环去做某件事

3、如何用循环

while循环的语法:while循环又称为条件循环。循环的次数取决于条件

　　while语法1：

while 条件:
    子代码1
    子代码2
    子代码3

print('start....')
while True:
     name=input('please your name>>: ')
     pwd=input('please your password>>: ')
     if name == 'egon' and pwd == '123':
         print('login successful')
     else:
         print('user or password err')
print('end...')

　　while语法2：如何结束while循环

方式一:操作while循环的条件让其结束
print('start....')
tag=True
while tag:
    name=input('please your name>>: ')
    pwd=input('please your password>>: ')
    if name == 'egon' and pwd == '123':
        print('login successful')
        tag=False
    else:
        print('user or password err')

print('end...')

方式二: break强行终止本层循环
count=1
while count < 6:
    print(count)
    count+=1


count=1
while True:
    if count > 5:
        break
    print(count)
    count+=1

print('start....')
while True:
    name=input('please your name>>: ')
    pwd=input('please your password>>: ')
    if name == 'egon' and pwd == '123':
        print('login successful')
        break
    else:
        print('user or password err')

print('end...')

 

输错三次则退出
方式一:
print('start....')
count=0
while count <= 2: #count=3
    name=input('please your name>>: ')
    pwd=input('please your password>>: ')
    if name == 'egon' and pwd == '123':
        print('login successful')
        break
    else:
        print('user or password err')
        count+=1

print('end...')

方式二
print('start....')
count=0
while True:
    if count == 3:
        print('输错的次数过多傻叉')
        break
    name=input('please your name>>: ')
    pwd=input('please your password>>: ')
    if name == 'egon' and pwd == '123':
        print('login successful')
        break
    else:
        print('user or password err')
        count+=1

print('end...')

　　while语法3：continue

count=1
while count < 6:
    if count ==  4:
        count+=1
        continue # 只能在cotinue同一级别之前加代码
    print(count)
    count+=1


while True:
    print('11111')
    print('22222')
    print('33333')
    continue # 不应该将continue作为循环体最后一步执行的代码

　　while语法4：else

count=1
while count < 6:
    if count == 4:
        break
    print(count)
    count+=1
else:
    print('会在while循环没有被break终止的情况下执行')


输错三次则退出之while+else的应用
print('start....')
count=0
while count <= 2: #count=3
    name=input('please your name>>: ')
    pwd=input('please your password>>: ')
    if name == 'egon' and pwd == '123':
        print('login successful')
        break
    else:
        print('user or password err')
        count+=1
else:
    print('输错的次数过多')

print('end...')

　　while语法5：循环嵌套

name_of_db='egon'
pwd_of_db='123'
print('start....')
count=0
while count <= 2: #count=3
    name=input('please your name>>: ')
    pwd=input('please your password>>: ')
    if name == name_of_db and pwd == pwd_of_db:
        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('请输入你的操作: ') #choice='1'
            if choice == '1':
                print('开始浏览商品....')
            elif choice == '2':
                print('正在添加购物车....')
            elif choice == '3':
                print('正在支付....')
            elif choice == '4':
                break
        break
    else:
        print('user or password err')
        count+=1
else:
    print('输错的次数过多')

print('end...')




# tag控制所有while循环
name_of_db='egon'
pwd_of_db='123'
tag=True
print('start....')
count=0
while tag:
    if count == 3:
        print('尝试次数过多')
        break
    name=input('please your name>>: ')
    pwd=input('please your password>>: ')
    if name == name_of_db and pwd == pwd_of_db:
        print('login successful')
        while tag:
            print("""
            1 浏览商品
            2 添加购物车
            3 支付
            4 退出
            """)
            choice=input('请输入你的操作: ') #choice='1'
            if choice == '1':
                print('开始浏览商品....')
            elif choice == '2':
                print('正在添加购物车....')
            elif choice == '3':
                print('正在支付....')
            elif choice == '4':
                tag=False

    else:
        print('user or password err')
        count+=1

print('end...')