if循环:有条件的执行,做出选择
例1:
1 a=42 2 if a<=10: 3 print('the number less than 10') 4 else: 5 print('thank you!')
例2:
1 people='M' 2 if people =='M': 3 print('girl')#if下的缩进归if管 4 else: 5 print('boy') 6 print('the end') #没有缩进不归if管
[root@localhost ~]# python 1.py girl the end
例3
1 a=103 2 if a>=100: 3 print('the number is larger or equal to 100') 4 else: 5 print('the number is less than 100')
[root@localhost ~]# python 1.py the number is larger or equal to 100
例4(if嵌套)
1 a='F' 2 b=30 3 if a=='M': 4 if b>=20: 5 print('gentleman') 6 else: 7 print('boy') 8 else: 9 if b<20: 10 print('girl') 11 else: 12 print('women')
[root@localhost ~]# python 1.py women
例5 分数分等级 0~60为no pass,60~70just pass,70~80good,80~90better,90~100best
1 record=92 2 if record >=60: 3 if record>=70: 4 if record>=80: 5 if record>=90 and record<=100: 6 print('best') 7 else: 8 print('better') 9 else: 10 print('good') 11 else: 12 print('just pass') 13 else: 14 print('no pass')
[root@localhost ~]# python 1.py best
while循环:重复某个功能多次
- 循环变量初始化(开始)——第一步
- 循环条件(给出终止的条件)——第二步
- 循环【可重复】语句()——第四步
- 循环的修正(修正条件)——第三步
例1
1 greetings=1 2 while greetings<=3: #这里记住了是<=而不是<-,不要和R混淆了 3 print('hello!'*greetings) 4 greetings=greetings+1
[root@localhost ~]# python 2.py hello! hello!hello! hello!hello!hello!
例2:打印100到200间的偶数
1 a=100 2 while a<=200: 3 if a%2 == 0: 4 print(a) 5 a=a+1 6 ####方法二 7 a=100 8 while a<=200: 9 print(a) 10 a=a+2
例3:输出1-100间3的倍数
1 a=1 2 while a<=100: 3 if a%3==0: 4 print(a) 5 a=a+1
例4:求1到100的和
1 a=1 2 sum=0 3 while a<=100: 4 if a==100: 5 print(sum) 6 sum=sum+a 7 a=a+1 8 ######## 9 a=1 10 sum=0 11 while a<=100: 12 a=a+1 13 sum=sum+a 14 print(sum) 15 (正确的方法)########### 16 a=1 17 sum=0 18 while a<=100: 19 sum=sum+a 20 a=a+1 21 print(sum) 22 ########### 23 a=1 24 sum=0 25 while a<=100: 26 sum=sum+a 27 a=a+1 28 print(sum) #注意print的位置缩进
例5:求1到100间的奇数和
1 a=1 2 sum=0 3 while a<=100: 4 if a%2==1: 5 sum = sum+a 6 a = a+1 7 print(sum)
[root@localhost ~]# python 1.py 2500
for循环:遍历列表中的每一个元素
例1
1 names=['a','b','c'] 2 for name in names: 3 print('hello!'+name)
[root@localhost ~]# python 1.py hello!a hello!b hello!c
例2
1 n=10 2 for i in range(n): 3 print(i)
题1:a=100,b=200,求a,b之间所有奇数的和