1. 什麽是循環

循環指的是一個重復做某件事的過程

2. 為何要有循環

為了讓計算機能夠像人一樣重復做某件事

3. 如何用循環

# while循環的語法：while循環又稱為條件循環，循環的次數取決於條件

while 條件

子代碼1

子代碼2

子代碼3

print（‘strat....‘）

while True:

name=input(‘please your name :‘)

pwd=input(‘please your password:‘)

if name == ‘summer‘ and pwd == ‘123‘:

print(‘login successful‘)

else:

print(‘user or password err‘)

print(‘end....‘)

如何結束while循環
方式一:操作while循環的條件讓其結束
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強行終止本層循環
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...‘)


輸錯三次則退出
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(‘輸錯的次數過多傻叉‘)
        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+continue:continue代表結束本次循環,直接進入下一次
count=1
while count < 6:
    if count ==  4:
        count+=1
        continue # 只能在cotinue同一級別之前加代碼
    print(count)
    count+=1


while True:
    print(‘11111‘)
    print(‘22222‘)
    print(‘333‘)
    continue # 不應該將continue作為循環體最後一步執行的代碼


while+else
count=1
while count < 6:
    if count == 4:
        break
    print(count)
    count+=1
else:
    print(‘會在while循環沒有被break終止的情況下執行‘)



輸錯三次則退出之while+else的應用
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(‘輸錯的次數過多‘)

print(‘end...‘)



while循環的嵌套
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 瀏覽商品
            2 添加購物車
            3 支付
            4 退出
            """)
            choice=input(‘請輸入你的操作: ‘) #choice=‘1‘
            if choice == ‘1‘:
                print(‘開始瀏覽商品....‘)
            elif choice == ‘2‘:
                print(‘正在添加購物車....‘)
            elif choice == ‘3‘:
                print(‘正在支付....‘)
            elif choice == ‘4‘:
                break
        break
    else:
        print(‘user or password err‘)
        count+=1
else:
    print(‘輸錯的次數過多‘)

print(‘end...‘)

tag控制所有while循環
name_of_db=‘egon‘
pwd_of_db=‘123‘
tag=True
print(‘start....‘)
count=0
while tag:
    if count == 3:
        print(‘嘗試次數過多‘)
        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 瀏覽商品
            2 添加購物車
            3 支付
            4 退出
            """)
            choice=input(‘請輸入你的操作: ‘) #choice=‘1‘
            if choice == ‘1‘:
                print(‘開始瀏覽商品....‘)
            elif choice == ‘2‘:
                print(‘正在添加購物車....‘)
            elif choice == ‘3‘:
                print(‘正在支付....‘)
            elif choice == ‘4‘:
                tag=False

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

print(‘end.....‘)

流程控制之while循環