练习3--数字和数学计算

1 常见的数学符号

• + plus，加号
• - minus，减号
•  / slash，斜杠
• * asterisk，星号
• % percent，百分号
• < less-than，小于号
• > greater-than，大于号
• <= less-than-equal，小于等于号
• >= greater-than-equal，大于等于号

2  一个例子：

python2语法下的代码：

   print "I will now count my chickens:"
   print "Hens", 25 + 30 / 6
   print "Roosters", 100 - 25 * 3 % 4
   print "Now I will count the eggs:"
   print 3 + 2 + 1 - 5 + 4 % 2 - 1 / 4 + 6
   print "Is it true that 3 + 2 < 5 - 7?"
   print 3 + 2 < 5 - 7
   print "What is 3 + 2?", 3 + 2
   print "What is 5 - 7?", 5 - 7
   print "Oh, that's why it's False."
   print "How about some more."
   print "Is it greater?", 5 > -2
   print "Is it greater or equal?", 5 >= -2
   print "Is it less or equal?", 5 <= -2

python3语法下的代码：

   print "I will now count my chickens:"
   print "Hens", 25 + 30 / 6
   print "Roosters", 100 - 25 * 3 % 4
   print "Now I will count the eggs:"
   print 3 + 2 + 1 - 5 + 4 % 2 - 1 / 4 + 6
   print "Is it true that 3 + 2 < 5 - 7?"
   print 3 + 2 < 5 - 7
   print "What is 3 + 2?", 3 + 2
   print "What is 5 - 7?", 5 - 7
   print "Oh, that's why it's False."
   print "How about some more."
   print "Is it greater?", 5 > -2
   print "Is it greater or equal?", 5 >= -2
   print "Is it less or equal?", 5 <= -2

3 运行结果：

python2语法下执行结果：

     $ python ex3.py
     I will now count my chickens:
     Hens 30
     Roosters 97
     Now I will count the eggs:
     7Is it true that 3 + 2 < 5 - 7?
     False
     What is 3 + 2? 5
     What is 5 - 7? -2
     Oh, that's why it's False.
     How about some more.
     Is it greater? True
     Is it greater or equal? True
     Is it less or equal? False
     $

 

python3语法下执行结果：

     I will now count my chickens:
     Hens 30.0
     Roosters 97
     Now I will count the eggs:
     6.75
     Is it true that 3 + 2 < 5 - 7?
     False
     What is 3 + 2? 5
     What is 5 - 7? -2
     Oh, that is why it's False.
     How about some more.
     Is it greater? True
     Is it greater or equal? True
     Is it less or equal? False

4 扩展

1. python2里面”/“运算小数点后的数会被丢掉，python3里面”/“运算可以输出小数点后的值，所以例子里面“鸡蛋的数量”运算结果不一样，一个是7，一个是6.75。（注意：可能python3自己完成了整数和浮点数的转换？）
2. 运算顺序：括号内优于（乘、除、取余%）优于（加、减），即PE(M&D)(A&S)
3. %号：表示取余数