4.2_控制流2while__range语句.docx

4.2_控制流2while__range语句.docx

1. while语句

Python 编程中 while 语句用于循环执行程序，即在某条件下，循环执行某段程序，以处理需要重复处理的相同任务。其基本形式为：

while判断条件：执行语句……

执行语句可以是单个语句或语句块。判断条件可以是任何表达式，任何非零、或非空（null）的值均为true。

当判断条件假false时，循环结束。

执行流程图如下：

python_while_loop

Gif 演示 Python while 语句执行过程

实例

#!/usr/bin/pythoncount =0while(count <9):print'The count is:',countcount =count + 1print"Good bye!"

 

运行实例 »

以上代码执行输出结果:

The countis:0The countis:1The countis:2The countis:3The countis:4The countis:5The countis:6The countis:7The countis:8Good bye!

while 语句时还有另外两个重要的命令 continue，break 来跳过循环，continue 用于跳过该次循环，break 则是用于退出循环，此外"判断条件"还可以是个常值，表示循环必定成立，具体用法如下：

 

 

 

设置 一直到 用户把 66 猜出来

#while example

 

number = 66

guess_flag = False

 

 

while guess_flag == False:

guess = int(input('Enter an integer : '))

if guess == number:

# New block starts here

guess_flag = True

 

# New block ends here

elif guess < number:

# Another block

print('No, the number is higher than that, keep guessing')

# You can do whatever you want in a block ...

else:

print('No, the number is a lower than that, keep guessing')

# you must have guessed > number to reach here

 

print('Bingo! you guessed it right.')

print('(but you do not win any prizes!)')

print('Done')

 

 

 

2. range语句

 

Code：

 

 

 

 

 

#For example 

 

number = 59

num_chances = 3

print("you have only 3 chances to guess")

 

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

    print("chance " + str(i))

    guess = int(input('Enter an integer : '))

    if guess == number:

        # New block starts here

        print('Bingo! you guessed it right.')

        print('(but you do not win any prizes!)') 

        break

 

        # New block ends here

    elif guess < number:

        # Another block

        print('No, the number is higher than that, keep guessing, you have ' + str(num_chances - i) + ' chances left')

        # You can do whatever you want in a block ...

    else:

        print('No, the number is lower than that, keep guessing, you have ' + str(num_chances - i) + ' chances left')

        # you must have guessed > number to reach here

 

 

print('Done')