Lesson 3-2 语句:循环语句
3.2 循环语句
3.2.1 while 循环语句
--- while 语句包含:关键字while、条件、冒号、while子句(代码块)。
--- 执行while 循环,首先判断条件是否为真,如果为假,结束while循环,继续程序中后面的语句,如果为真,执行while子句的代码块,执行完后调回到while循环开始的地方,重新判断条件是否为真,如果为真,执行while子句的代码块,一遍一遍的循环执行,直至条件为假。
1 a = 1 2 while a < 10 : 3 print(a) 4 a = a +1 5 6 print('Hello world!') 7 8 结果: 9 /usr/bin/python3.7 /home/jlu/Projects/Python/untitled/2019-4-21/循环语句.py 10 1 11 2 12 3 13 4 14 5 15 6 16 7 17 8 18 9 19 Hello world! 20 21 Process finished with exit code 0
&、注意while 语句和if 语句的区别,当条件为真时,while语句执行完一遍后会返回开始点,if 语句执行完一遍后不返回,继续往下执行。
3.2.2 for 循环语句
--- for 语句包含:for 关键字、一个变量名、in关键字、可迭代对象、冒号、for子句(代码块)。
--- for 语句含义:执行迭代(遍历)可迭代对象次数的for子句代码块。
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1 lis = [1, 2, 3, 4, 5] 2 for i in lis: 3 print(i) 4 5 total = 0 6 for num in range(101): 7 total = total + num 8 print(total) 9 10 结果: 11 /usr/bin/python3.7 /home/jlu/Projects/Python/untitled/2019-4-21/循环语句.py 12 1 13 2 14 3 15 4 16 5 17 5050 18 19 Process finished with exit code 0
3.2.3 break 语句
--- break 语句只包含break 关键字,通常放在if 语句的代码块中使用,用于满足一定条件时,立即结束当前迭代,并提前结束循环。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 total = 0 2 for num in range(101): 3 total = total + num 4 if total > 2000 : 5 break 6 7 print(num,total) 8 9 10 结果: 11 /usr/bin/python3.7 /home/jlu/Projects/Python/untitled/2019-4-21/循环语句.py 12 63 2016 13 14 Process finished with exit code 0
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 total = 0 2 num = 1 3 while num < 101 : 4 total = total + num 5 num = num +1 6 if total > 2000 : 7 break 8 9 print(num,total) 10 11 12 结果: 13 /usr/bin/python3.7 /home/jlu/Projects/Python/untitled/2019-4-21/循环语句.py 14 64 2016 15 16 Process finished with exit code 0
3.2.4 continue 语句
--- continue 语句只包含continue 关键字,它结束当前迭代,并跳回到迭代开头处,继续进行循环条件判断,条件为真时继续进入循环。
1 num = 1 2 while num : 3 num = num * num + 1 4 print(str(num) + '-while') 5 if num < 100 : 6 continue 7 print(str(num) + '-continue') 8 if num > 1000 : 9 break 10 print(str(num) + '-break') 11 print(str(num) + '-end') 12 13 14 结果: 15 /usr/bin/python3.7 /home/jlu/Projects/Python/untitled/2019-4-21/循环语句.py 16 2-while 17 5-while 18 26-while 19 677-while 20 677-continue 21 677-break 22 458330-while 23 458330-continue 24 458330-end 25 26 Process finished with exit code 0
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