# Math
> 2 ** 3 # 次方
 => 8
 
=begin
  Addition (+)
  Subtraction (-)
  Multiplication (*)
  Division (/)
  Exponentiation (**)
  Modulo (%)
=end
> 9.9.integer?
 => false
 
> -5.abs
 => 5
 
> 5.6.round # 取最近的整數/四捨五入
 => 6
 
> 9.9.floor	# 取整數/無條件捨去
 => 9 

> 2312.22.ceil   # 取整數/無條件進位
=> 2313

> 2.next
 => 3
# 二元運算
n & num
n | num
n ^ num (XOR)
n << num (向左位移)
n >> num (向右位移)

Reference: http://www.tutorialspoint.com/ruby/ruby_builtin_functions.htm