python:while循环语句及练习题

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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

https://www.cnblogs.com/bug132294/p/11774710.html

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