3.运算符与表达式，控制流

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时间：2018年12月8日14:56:25

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表达式包括运算符与操作数

1、运算符

2、求值顺序

控制流（3种）

1、if语句

number = 23
guess = int(input('enter an number:'))
if guess == number:  #注意别忘记冒号
    print('yes!')
    print('(but you do not win any prizes!)')
elif guess < number:
    print('no,it is a little higher than that')
else:
    print('no, it is a little lower than that')
print('done')  #这一句在if结束后执行

  2.while语句

number = 23
running = True

while running:
    guess = int(input('enter an number:'))
    if guess == number:  #注意别忘记冒号
        print('yes!')
        running = False
    elif guess < number:
        print('no,it is a little higher than that')
    else:
        print('no, it is a little lower than that')
else:
    print('while is over.')
print('done')  #这一句在if结束后执行

3、for循环

for i in range(1,5):
    print(i)
else:
    print('the for loop is over')

4、break语句

        用于中断循环语句 的执行，如果中断了for或while循环，相应循环中的else块都将不会被执行。

while True:
    s = input('Enter something:')
    if s == 'quit':
        break#跳出while循环
    print('length of the string is',len(s))
print('done')

5、continue语句

       跳过当前循环块中的剩余语句，并继续该循环的下一次迭代。

while True:
    s = input('enter somethong:')
    if s == 'quit':
        break#退出while循环
    if len(s)<3:
        print('too small')
        continue#继续下一次while
    print('input is of sufficient length')
print('done')

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结束：2018年12月8日17:06:40

进度：59/153