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if、for、while语句

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表达式if ... else

场景一、用户登陆验证

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 # 提示输入用户名和密码    # 验证用户名和密码 #     如果错误,则输出用户名或密码错误 #     如果成功,则输出 欢迎,XXX!     #!/usr/bin/env python # -*- coding: encoding -*-    import getpass       name = raw_input('请输入用户名:') pwd = getpass.getpass('请输入密码:')    if name == "alex" and pwd == "cmd":     print("欢迎,alex!") else:     print("用户名和密码错误")

场景二、猜年龄游戏

在程序里设定好你的年龄,然后启动程序让用户猜测,用户输入后,根据他的输入提示用户输入的是否正确,如果错误,提示是猜大了还是小了

1 2 3 4 5 6 7 8 9 10 11 12 13 14 #!/usr/bin/env python # -*- coding: utf-8 -*-     my_age = 28   user_input = int(input("input your guess num:"))   if user_input == my_age:     print("Congratulations, you got it !") elif user_input < my_age:     print("Oops,think bigger!") else:     print("think smaller!")
外层变量,可以被内层代码使用 内层变量,不应被外层代码使用

for循环(loop)

 

最简单的循环10次

1 2 3 4 5 6 #_*_coding:utf-8_*_ __author__ = 'Alex Li'     for in range(10):     print("loop:", i )

输出:

1 2 3 4 5 6 7 8 9 10 loop: 0 loop: 1 loop: 2 loop: 3 loop: 4 loop: 5 loop: 6 loop: 7 loop: 8 loop: 9

需求一:还是上面的程序,但是遇到小于5的循环次数就不走了,直接跳入下一次循环

1 2 3 4 for in range(10):     if i<5:         continue #不往下走了,直接进入下一次loop     print("loop:", i )

需求二:还是上面的程序,但是遇到大于5的循环次数就不走了,直接退出

1 2 3 4 for in range(10):     if i>5:         break #不往下走了,直接跳出整个loop     print("loop:", i )

 

while循环(loop)  

 有一种循环叫死循环,一经触发,就运行个天荒地老、海枯石烂。

海枯石烂代码

1 2 3 4 5 count = 0 while True:     print("你是风儿我是沙,缠缠绵绵到天涯...",count)     count +=1     

其实除了时间,没有什么是永恒的,死loop还是少写为好 

上面的代码循环100次就退出吧

1 2 3 4 5 6 7 8 count = 0 while True:     print("你是风儿我是沙,缠缠绵绵到天涯...",count)     count +=1     if count == 100:         print("去你妈的风和沙,你们这些脱了裤子是人,穿上裤子是鬼的臭男人..")         break    

回到上面for 循环的例子,如何实现让用户不断的猜年龄,但只给最多3次机会,再猜不对就退出程序。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 #!/usr/bin/env python # -*- coding: utf-8 -*-     my_age = 28   count = 0 while count < 3:     user_input = int(input("input your guess num:"))       if user_input == my_age:         print("Congratulations, you got it !")         break     elif user_input < my_age:         print("Oops,think bigger!")     else:         print("think smaller!")     count += 1 #每次loop 计数器+1 else:     print("猜这么多次都不对,你个笨蛋.")

 

 
break和continue的区别?
for i in range(10):
print('----', i)
for j in range(10):
print(j)
if j > 5:
break # 结束当前内部循环
# continue # 跳出当前循环,继续执行下次循环

 

 条件判断语句:
使用if...else...
_username = 'lsj'
_password = 'abc123'
username = input("username:")
password = input("password:")
print(username, password)

# 验证用户名和密码是否正确,使用if...else
if _username == username and _password == password:
print("Welcome user {name} login...".format(name=username))
else:
print("Invalid username or password!!!")

注意:缩进的错误提示:
IndentationError: unindent does not match any outer indentation level
缩进错误:unindent不匹配任何外部缩进级别

# 猜数字小游戏
# 定义自己的年龄23岁
age_of_lsj = 23
# 定义要猜测的年龄
# guess_age = int(input("guess age:"))

# 使用if判断
# if guess_age == age_of_lsj:
# print("yes,you got it!!!")
# elif guess_age > age_of_lsj:
# print("think smaller!!! ")
# elif guess_age < age_of_lsj:
# print("think bigger!!!")

# 使用while循环可以执行多次操作
# count = 0
# while True: # 当TRUE时候执行下面
# print("count :", count)
# count += 1 # count = count + 1

# 可以无限次数猜测
# while True:
# guess_age = int(input("guess age:"))
# if guess_age == age_of_lsj:
# print("yes,you got it!!!")
# break
# elif guess_age > age_of_lsj:
# print("think bigger!!! ")
# else:
# print("think smaller!!!")

# 限制3次机会猜测
count = 0 # 做一个计数器
# while True:
# if count == 3:
# print("执行结束")
# break
while count < 3:
guess_age = int(input("guess age:"))
if guess_age == age_of_lsj:
print("yes,you got it!!!")
break
elif guess_age > age_of_lsj:
print("think bigger!!! ")
else:
print("think smaller!!!")
count += 1

# if count == 3:
else:
print("you have tried too many times..fuck off")


# 认识for循环
for i in range(0, 10, 2):
print("loop", i)

for循环优化while循环的版本
age_of_lsj = 23
for i in range(10):
guess_age = int(input("guess age:"))
if guess_age == age_of_lsj:
print("yes,you got it!!!")
break
elif guess_age > age_of_lsj:
print("thi1nk bigger!!! ")
else:
print("think smaller!!!")
else:
print("you have tried too many times..fuck off")
 
# 需求:
# 1、每次当输入第三次错误时候,提问是否继续。
# 2、当输入回车或者任意一个键盘时候继续玩游戏。
# 3、当输入n的时候结束游戏

age_of_lsj = 23
count = 0
while count < 3:
guess_age = int(input("guess_age:"))
if guess_age == age_of_lsj:
print("yes,you got it!!!")
break
elif guess_age > age_of_lsj:
print("think bigger!!!")
else:
print("think smaller!!!")
count += 1
if count == 3:
countine_confirm = input("do you want to keep guessing..?")
if countine_confirm != 'n':
count = 0

标签:语句,count,guess,age,while,print,input,loop
来源: https://www.cnblogs.com/liunaixu/p/16512608.html