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本帖最后由 和vvv 于 2017-6-20 12:23 编辑
04 Python控制流与小实例
一、三种控制流概述
程序执行流程我们叫做程序的控制流,Python有三种基本控制流:
二、if语句
if语句是一种条件分支结构语句。打开idle,“Ctrl+N”输入代码并保存,按F5执行:- a = 10
- b = 1
- if a > b:
- print(a) #输出10
复制代码 if语句可以嵌套使用,要注意代码的缩进:- a = 10
- b = 1
- if a > b:
- print(a) #输出10
- if b < 2:
- print(b) #输出1
复制代码 if语句通常与elif、else一起使用:- #获得用户输入
- temp = input("输入一个整数:")
- #将输入转化为整数
- n = int(temp)
- if n>0 and n % 2 ==0:
- print("用户输入的是偶数")
- elif n>0 and n%2 != 0:
- print("用户输入的是奇数")
- else:
- print("用户输入的是负数")
复制代码
三、while语句
while语句是一种循环结构的语句。- a = 0
- while a < 10:
- print("赞")
- a += 1 #a=a+1
复制代码- ======== RESTART: F:/Python/procedure/if.py ========
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- >>>
复制代码 需要注意循环结束条件的控制,不然可能会造成死循环。
四、for语句
for 语句也是一种循环结构的语句。
1.遍历列表- l = ["aa","b","c","d"]
- for i in l:
- print(i)
复制代码- >>>
- ======== RESTART: F:/Python/procedure/if.py ========
- aa
- b
- c
- d
- >>>
复制代码 2.进行常规循环
- for i in range(0,10): #range产生0,1,2,...,9
- print(i)
复制代码- ======== RESTART: F:/Python/procedure/if.py ========
- 0
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- >>>
复制代码- for i in range(0,10):
- print("赞")
复制代码- >>>
- ======== RESTART: F:/Python/procedure/if.py ========
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- 赞
- >>>
复制代码
五、中断结构
所谓中断结构,指的是中途退出的一种结构。常用continue和break语句。
1.break:全部直接退出,整个循环都中断- for i in range(0,10):
- if i == 5:
- break
- print(i)
复制代码- >>>
- ======== RESTART: F:/Python/procedure/if.py ========
- 0
- 1
- 2
- 3
- 4
- >>>
复制代码 2.continue:中断一次循环,继续下一次循环- for iin range(0,10):
- if i == 5:
- continue
- print(i)
复制代码
- >>>
- ======== RESTART: F:/Python/procedure/if.py ========
- 0
- 1
- 2
- 3
- 4
- 6
- 7
- 8
- 9
- >>>
复制代码
六、输出乘法口诀- for i in range(1,10):
- for j in range(1,i+1):
- print(i,"×",j,"=",i*j,end=" ")
- print("\n")
复制代码 结果:
>>>======== RESTART: F:/Python/procedure/if.py ========
1 × 1 = 1
2 × 1 = 2 2 × 2 = 4
3 × 1 = 3 3 × 2 = 6 3 × 3 = 9
4 × 1 = 4 4 × 2 = 8 4 × 3 = 12 4 × 4 = 16
5 × 1 = 5 5 × 2 = 10 5 × 3 = 15 5 × 4 = 20 5 × 5 = 25
6 × 1 = 6 6 × 2 = 12 6 × 3 = 18 6 × 4 = 24 6 × 5 = 30 6 × 6 = 36
7 × 1 = 7 7 × 2 = 14 7 × 3 = 21 7 × 4 = 28 7 × 5 = 35 7 × 6 = 42 7 × 7 = 49
8 × 1 = 8 8 × 2 = 16 8 × 3 = 24 8 × 4 = 32 8 × 5 = 40 8 × 6 = 48 8 × 7 = 56 8 × 8 = 64
9 × 1 = 9 9 × 2 = 18 9 × 3 = 27 9 × 4 = 36 9 × 5 = 45 9 × 6 = 54 9 × 7 = 63 9 × 8 = 72 9 × 9 = 81
>>> 逆向输出乘法口诀:
- for i in range(9,0,-1):
- for j in range(1,i+1):
- print(i,"×",j,"=",i*j,end=" ")
- print("\n")
复制代码 结果:
>>>
======== RESTART: F:/Python/procedure/if.py ========
9 × 1 = 9 9 × 2 = 18 9 × 3 = 27 9 × 4 = 36 9 × 5 = 45 9 × 6 = 54 9 × 7 = 63 9 × 8 = 72 9 × 9 = 81
8 × 1 = 8 8 × 2 = 16 8 × 3 = 24 8 × 4 = 32 8 × 5 = 40 8 × 6 = 48 8 × 7 = 56 8 × 8 = 64
7 × 1 = 7 7 × 2 = 14 7 × 3 = 21 7 × 4 = 28 7 × 5 = 35 7 × 6 = 42 7 × 7 = 49
6 × 1 = 6 6 × 2 = 12 6 × 3 = 18 6 × 4 = 24 6 × 5 = 30 6 × 6 = 36
5 × 1 = 5 5 × 2 = 10 5 × 3 = 15 5 × 4 = 20 5 × 5 = 25
4 × 1 = 4 4 × 2 = 8 4 × 3 = 12 4 × 4 = 16
3 × 1 = 3 3 × 2 = 6 3 × 3 = 9
2 × 1 = 2 2 × 2 = 4
1 × 1 = 1
>>>
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