第6节.用户输入和while循环

6.1函数input()

简单的输入

massage=input("Tell me something,and I will repeat it back to you:")
print(massage)

输入数值

age=input("How old are you?")
print(age)
#此时用户输入会被默认解释为字符串
​
age=input("How old are you?")
age=int(age)
#此时就将用户输入指定成了数值
print(age)
​
#更加简便的指定用户输入
age=int(input("How old are you?"))
print(int(age))

6.2求模运算符

A=4%3
print(A)
#将两个数相除并返回余数

6.3while循环

while循环简介

current_number=1
while current_number<=5:   #循环从1数到5
    print(current_number)
    current_number +=1

让用户选择何时退出

prompt="\nTell me something, and I will repeat it back to you:"
prompt+="\nEnter 'quit' to end the program. "
message=""     #使用空字符定义变量，用于接收输入的字符串
while message != 'quit':
    message=input(prompt)
    print(message)

上述代码的缺点是将quit也打印了出来，下面用一个if语句优化它

prompt="\nTell me something, and I will repeat it back to you:"
prompt+="\nEnter 'quit' to end the program. "
message=""
while message != 'quit':
    message=input(prompt)
    if message !='quit':
        print(message)

使用标志

prompt="\nTell me something, and I will repeat it back to you:"
prompt+="\nEnter 'quit' to end the program. "
active=True
while active:
    message=input(prompt)
    if message=='quit':
        active=False
    else:
        print(message)

使用break函数退出循环

prompt="\nTell me something, and I will repeat it back to you:"
prompt+="\nEnter 'quit' to end the program. "
while True:
    city=input(prompt)
    if city == 'quit':
        break
        #break语句也可以用于退出遍历列表或字典的for循环
        else:
            print(f"I'd love to go to {city.title()}")
​
​

在循环中使用continue

current_number=0
while current_number <10:
    current_number += 1
    if current_number%2==0:
        continue
    print(current_number)

当程序陷入无限循环时，按CTRL+C可以关闭程序

6.4使用while循环处理列表和字典

在列表之间移动元素

#首先，创建一个待验证用户列表
#和一个用于存储已验证用户的空列表
unconfirmed_users = ['alice', 'brian', 'candace']
confirmed_users = []
​
#验证每个用户，直到没有未验证用户为止
#将每个经过验证的列表都移到已验证用户列表中
while unconfirmed_users:
    current_user = unconfirmed_users.pop()
    print("Verifying user: " + current_user.title())
confirmed_users.append(current_user)   #将元素添加到已验证列表中
​
#显示所有已验证的用户
print("\nThe following users have been confirmed:")
for confirmed_user in confirmed_users:
    print(confirmed_user.title())

删除为特定值的所有列表元素

pets = ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
print(pets)
while 'cat' in pets:
    pets.remove('cat')
print(pets)

使用用户输入来填充字典

responses = {}
#设置一个标志，指出调查是否继续
polling_active = True
​
while polling_active:
#提示输入被调查者的名字和回答
    name = input("\nWhat is your name? ")
    response = input("Which mountain would you like to climb someday? ")
#将答卷存储在字典中
    responses[name] = response
#看看是否还有人要参与调查
    repeat = input("Would you like to let another person respond? (yes/ no) ")
    if repeat == 'no':
        polling_active = False
​
#调查结束，显示结果
print("\n--- Poll Results ---")
for name, response in responses.items():
    print(name + " would like to climb " + response + ".")