python:while循环语句及练习题

while循环语句及练习题

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。

实例:

count = 0 while (count < 9): print ('The count is:', count) count = count + 1 print("Good bye!") 

运行结果:

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

continue 和 break 用法

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:

i = 1 while i < 10: i += 1 if i%2 > 0: # 非双数时跳过输出 continue print(i) # 输出双数246810 

运行结果:

2 4 6 8 10 

i = 1 while 1: # 循环条件为1必定成立 print(i) # 输出1~10 i += 1 if i > 10: # 当i大于10时跳出循环 break

运行结果:

1 2 3 4 5 6 7 8 9 10 

无限循环

如果条件判断语句永远为 true,循环将会无限的执行下去,如下实例:

var = 1 while var == 1 : # 该条件永远为true,循环将无限执行下去 num = input("Enter a number :") print ("You entered: ", num) print ("Good bye!") 
Enter a number :3 You entered: 3 Enter a number :4 You entered: 4 Enter a number :5 You entered: 5 Enter a number :6 You entered: 6 Enter a number :7 You entered: 7 Enter a number :8 You entered: 8 Enter a number :100 You entered: 100 Enter a number :Traceback (most recent call last): File "c:/1.py", line 76, in <module> # num = input("Enter a number :") KeyboardInterrupt 

注意:以上的无限循环你可以使用 CTRL+C 来中断循环。

循环使用 else 语句

在 python 中,while … else 在循环条件为 false 时执行 else 语句块:

count = 0 while count < 5: print (count, " is less than 5") count = count + 1 else: print (count, " is not less than 5") 

运行结果:

0 is less than 5 1 is less than 5 2 is less than 5 3 is less than 5 4 is less than 5 5 is not less than 5 

相关练习题

1.输出1,2,3,4,5,6,8,9,10
count = 1 while count <= 10:   if count == 7:     pass   else:     print(count)   count = count + 1 
2.输出1-100所有数的和
n = 1 m = 0 while n < 101:   m = m + n   n = n + 1 print(m) 
3.输出100以内所有奇数
n = 1 while n < 101:   temp = n % 2   if temp == 0:     print(n)   else:     pass   n = n +1 
4.输出1-2+3-4+5…..99所有数的和
n = 1 m = 0 while n < 100:   temp = n % 2   if temp == 0:     m = m - n   else:     m = m + n   n = n + 1 print(m) 

参考资料:

1.Python While 循环语句 | 菜鸟教程:https://www.runoob.com/python/python-while-loop.html

    原文作者:bug132294
    原文地址: https://www.cnblogs.com/bug132294/p/11774710.html
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