day04之流程控制

if语句：

 if 条件1：

     pass

 elif 条件2：

    pass

 elif 条件3：

    pass

 else：

    pass

if 条件语句中，先判断条件1，如果满足条件1，则执行第二行代码，第二行执行完后if条件语句结束。

示例：用户取款机菜单用户选择界面：

from time import sleep

num = input("Please input your chioce:")

if num == "":

    print("取款中.....")

    sleep(3)

    print("取款完成！")

elif num == "":

    print("存款中....")

    sleep(3)

    print("存款完成！")

elif num == "":

    print("查询中....")

    sleep(3)

    print("查询完成！")

elif num == "":

    print("退出中....")

    sleep(1)

    print("已退出!")

else:

    print("Please input the right nummber!")

——————————————————————————————————————————

while循环：while 条件：用于循环执行某段代码

示例：用户登陆界面

while True:

    name = input("Please input your name :")

    pwd = input("Please input your password :")

    if name == "egon" and pwd == "":

        print("login  successful")

    else:

        print("name or password Error! Please input again!")

while循环可以嵌套while循环

示例：用户登陆退出

name = "egon"

password = ""

tag = True

while tag:

    User_name = input("Name >>>")

    User_pwd = input("Password >>>")

    if User_name.lower() == name and User_pwd == password:

        while tag:

            Request = input("Request >>>")

            if Request.lower() == "quit":

                print("Over")

                tag = False

    else:

        print("Name or Password Error,Please input again")

while和break，continue搭配使用

示例1：while和break搭配用户登陆退出

name = "egon"
password = "123"

while True:

    User_name = input("Name >>>")

    User_pwd = input("Password >>>")

    print(User_name.lower())

    if name.lower() == User_name and password == User_pwd:

        print("login successful!")

        request = input("Request >>>")

        while True:

            if request.lower() =="quit":

                print("Over!")

                break

        break

    else:

        print("Name or Password Error,Please ipnut again!")

循环中遇到break即退出当前循环执行循环外代码。

示例2：while和continue搭配使用，筛选输出值

while True:

    val = input("请输入数据以逗号分隔：")

    val = val.split(",")

    try:

        val = list(map(int,val))

    except ValueError as e:

        continue

    count = 1

    while count < 20:

        if count in val:

            count += 1

            continue

        else:

            print(count)

            count += 1

continue的功能是当执行到continue时不再执行continue以后子代码块语句直接回到循环判断，进行下一次循环

当val = list（map（int，val））语句出错时执行continue语句，当执行到continue语句时立马重新回到当前循环判断条件。

——————————————————————————————————————————

for循环：for循环可以实现的功能while循环统统可以实现，但在某些场景，for循环更简洁，比如取值

如：

L = [1,2,3,4]

for i in L:

   print(i)

>>>

1

2

3

4

for 嵌套

示例1：打印99乘法表

L = []

for i in range(1, 10):

    for j in range(1, i + 1):

        m = "%s * %s = %s" % (i, j, i*j)

        L.append(m)

    print(*L)

    L = []

>>>>

C:\Users\DELL\AppData\Local\Programs\Python\Python37\python3.exe C:/Users/DELL/PycharmProjects/untitled1/ad.py

1 * 1 = 1

2 * 1 = 2 2 * 2 = 4

3 * 1 = 3 3 * 2 = 6 3 * 3 = 9

4 * 1 = 4 4 * 2 = 8 4 * 3 = 12 4 * 4 = 16

5 * 1 = 5 5 * 2 = 10 5 * 3 = 15 5 * 4 = 20 5 * 5 = 25

6 * 1 = 6 6 * 2 = 12 6 * 3 = 18 6 * 4 = 24 6 * 5 = 30 6 * 6 = 36

7 * 1 = 7 7 * 2 = 14 7 * 3 = 21 7 * 4 = 28 7 * 5 = 35 7 * 6 = 42 7 * 7 = 49

8 * 1 = 8 8 * 2 = 16 8 * 3 = 24 8 * 4 = 32 8 * 5 = 40 8 * 6 = 48 8 * 7 = 56 8 * 8 = 64

9 * 1 = 9 9 * 2 = 18 9 * 3 = 27 9 * 4 = 36 9 * 5 = 45 9 * 6 = 54 9 * 7 = 63 9 * 8 = 72 9 * 9 = 81

示例2：金字塔

分析：

        *             #第一行4个空格，1个*

      * * *           #第二行3个空格，3个*

    * * * * *         #第三行2个空格，5个*

  * * * * * * *       # ....

* * * * * * * * *

max_level = 5

L = []

for current_level in range(1 , max_level+1):

    # print(current_level)

    for m in range(max_level-current_level):

        L.append(" ")#将空格装入列表

    for n in range(2*current_level-1):

        L.append("*")#将*装入列表

    print(*L)

    L = [] #里层for循环完一次重新定义L为空列表，准备装下一次的循环的元素

——————————————————————————————————————————

while,for,break等综合应用

from time import sleep

name = "egon"

password = ""

while True:

    User_name = input("Please input your ID:")

    User_pwd = input("Please input your Password:")

    if User_name == name and User_pwd == password:

        print("login successful")

        print("""

        1 取款

        2 存款

        3 查询

        4 退出

                    """)

        while True:

            num = input("Please input your chioce:")

            if num == "":

                print("取款中.....")

                sleep(3)

                print("取款完成！")

            elif num == "":

                print("存款中....")

                sleep(3)

                print("存款完成！")

            elif num == "":

                print("查询中....")

                sleep(3)

                print("查询完成！")

            elif num == "":

                print("退出中....")

                sleep(1)

                print("已退出!")

                break

            else:

                print("Please input the right nummber!")

        break

>>>>>

C:\Users\DELL\AppData\Local\Programs\Python\Python37\python3.exe C:/Users/DELL/PycharmProjects/untitled1/ad.py

Please input your ID:egon

Please input your Password:

login successful

        1 取款

        2 存款

        3 查询

        4 退出

Please input your chioce:

取款中.....

取款完成！

Please input your chioce:

存款中....

存款完成！

Please input your chioce:

查询中....

查询完成！

Please input your chioce:

退出中....

已退出!

Process finished with exit code 0

巴特西

day04之流程控制

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