day05 while及for循环

01.流程控制之while循环

①   什么是循环

循环就是重复做某件事

②   为何要有循环

控制计算机能够像人一样重复做某件事

③   循环的使用

基本语法：

While 条件：

            代码1

            代码2

         代码3

……..

基本用法：

#打印0-10

count=0

while count <= 10:

    print('loop',count)

    count+=1

 

#打印0-10之间的偶数

count=0

while count <= 10:

    if count%2 == 0:

        print('loop',count)

    count+=1

 

#打印0-10之间的奇数

count=0

while count <= 10:

    if count%2 == 1:

        print('loop',count)

    count+=1

④   死循环

import time

num=0

while True:

    print('count',num)

    time.sleep(1)

    num+=1　　

⑤   结束循环的两种方式

方式一: 把条件改为False

特点：等到本次循环体代码运行完毕后，下一次循环判断条件时才会生效

i=0

tag=True

 

while tag:

    if i == 5:

        tag=False

 

    print(i)

    i+=1

 

方式二：break代表结束本层循环

特点：立即干掉本层while循环

i=0

tag=True

 

while tag:

    if i == 5:

        tag=False

        # break

    print(i)

i+=1

 

⑥   多层循环嵌套

方式一：

tag = True

while tag:

    while tag:

        while tag:

            tag = False

 

方式二

while True:

    while True:

        while True:

            break

        break

    break

 

案例1

tag = True

while tag:

    inp_user = input("username>>>: ")

    inp_pwd = input("password>>>: ")

 

    if inp_user == "egon" and inp_pwd == "123":

        print('login successful')

        # break

        tag = False

    else:

        print('username or password error')

 

    # print('=======================>')

 

案例2

while True:

    inp_user = input("username>>>: ")

    inp_pwd = input("password>>>: ")

 

    if inp_user == "egon" and inp_pwd == "123":

        print('login successful')

        while True:

            print("""

            0 退出

            1 取款

            2 存款

            3 转账

            """)

            choice = input("请输入您的命令编号：")

            if choice == "0":

                break

            elif choice == "1":

                print("正在取款。。。")

            elif choice == "2":

                print("正在存款。。。")

            elif choice == "3":

                print("正在转账。。。")

            else:

                print("输入的指令不存在")

        break

    else:

        print('username or password error')

 

 

⑦   while+continue：结束本次循环，直接进入下一次

count = 0

while count < 6:

    if count == 2 or count == 4:

        # break

        count += 1

        continue  # continue同级别之后千万别写代码，写了也不会运行

    print(count)

    count += 1

 

案例

while True:

    inp_user = input("username>>>: ")

    inp_pwd = input("password>>>: ")

 

    if inp_user == "egon" and inp_pwd == "123":

        print('login successful')

        break

    else:

        print('username or password error')

        # continue  # continue一定不要加在最后一步

 

⑧   while+else：else的子代码块会在while循环正常死亡时运行，没有被break干掉就叫正常死亡

count = 0

while count < 5:

    if count == 2:

        # count += 1

        # continue

        break

    print(count)

    count += 1

else:

print('====>')

 

02．流程控制之for循环

①．for，语法如下

　　for x in names:

    print(x)

 

dic={"k1":111,'K2':2222,"k3":333}

for x in dic:

    print(x,dic[x])

 

for x in "hello":

    print(x)

 

for x,y in [["name","egon"],["age",18],["gender","male"]]:  # x,y = ['name', 'egon']

    print(x,y)

 

②．break与continue

for i in [11,22,33,44,55]:

    if i == 33:

        break

    print(i)

 

for i in [11,22,33,44,55]:

    if i == 33:

        continue

    print(i)

 

③．for+else

for i in [11,22,33,44,55]:

    if i == 33:

        break

    print(i)

else:

    print('++++++++>')

 

 

④．range()

i=0

while i < 3:

    print(111)

    print(222)

    print(333)

    i+=1

 

 

for x in range(3):

    print(111)

    print(222)

    print(333)