python-- branch statement

if statement:

1. boolData types: true and false, only two values, that is, Trueand False.
2. ifStatement uses the syntax:

   if False:
       print('success')
   else:
       print('fail')
   

3. else: Statement:

   if False:
       print('success')
   else:
       print('fail')
   

4. Comparison operators:

   • a==b: A and b are equal.

         a = 1
         b = 2
         if a == b:
             print('equal')
         else:
             print('not equal')
     

   • a!=b: A and b are not equal.

         username = input(u'请输入用户名：')
         if username != 'zhiliao':
             print('您的用户是没有被加入到黑名单，可以正常使用')
         else:
             print('您的用户被加入到黑名单，不能正常使用')
     

   • a>b: A is greater than b.

         age = 17
         if age > 17:
             print('您可以进入到网吧了')
         else:
             print('您年龄未满18岁，不能进入网吧')
     

   • a<b: A is less than b.

         age = 17
         if age < 18:
             print('您的年龄未满18岁，不能进入网吧')
         else:
             print('您可以进入到网吧了')
     

   • a>=b: A not less than a b.

         age = 18
         if age >= 18:
             print('您可以进入到网吧了')
         else:
             print('您的年龄未满18岁，不能进入网吧')
     

   • a<=b: A is less than equal to b.

         age = 18
         if age <= 17:
             print('您的年龄未满18岁，不能进入网吧')
         else:
             print('您可以进入到网吧了')
     

   • 条件a and 条件b: Only a condition and conditions are met b was set up:

         age = input('请您输入年龄：')
         age = int(age)
         if age >= 15 and age <= 24:
             print('您是一个青年人')
         else:
             print('您不是一个青年人')
     

   • 条件a or 条件b: As long as satisfying a condition or a condition in b, on the establishment:

         if age < 15 or age > 24:
             print('您不是一个青年人')
         else:
             print('您是一个青年人')
     

   • not 条件a: If a condition is True, it returns False. If the condition b is False, then return True:

         person1 = '中国人'
         person2 = '南非'
     
         if not person2 == '中国人':
             print('不可以上战舰')
         else:
             print('可以上战舰')
     

elif statement:

   index = input('请输入星期数字：')

   index = int(index)

   if index == 0:
       print('星期天')
   elif index == 1:
       print('星期一')
   elif index == 2:
       print('星期二')
   elif index == 3:
       print('星期三')
   elif index == 4:
       print('星期四')
   elif index == 5:
       print('星期五')
   else:
       print('星期六')