if、if elif判断

1、if.py

 #coding=utf-8
 user = 'alex'
 passwd = 'alex3714'

 username = input('username:')
 password = input('password:')

 if user == username:
   print ('username is correct...')
 if passwd == password:
   print ('Welcome login...')
 else:
   print('password is invalid...')
 else:
   print('连用户名都没蒙对，滚粗。。。')

2、if优化版.py

 #coding=utf-8
 user = 'alex'
 passwd = 'alex3714'

 username = input('username:')
 password = input('password:')

 if user == username and passwd == password:
   print ('Welcome login...')
 else:
   print('Invalid username or password...')

3、猜年龄

guess_age.py

 #coding=utf-8
 age = 22
 guess_num = int(input('input your guess num:'))
 if guess_num == age:
   print ('Congratulations！you got it.')
 elif guess_num > age:
   print ('Think smaller!')
 else:
   print ('Think big...')