From: Dan Zwell <dzwell@...>
Date: 2007-08-24T14:10:43+09:00
Subject: Re: Combinations of numbers/operators?

Donald Patch wrote:
> Let's say I have an array consisting of 4 integers i.e. 1,2,3,4. I would
> like to print every combination of these numbers using math operators
> such as +-/*. The output should resemble something like:
> 
> 1+2+3+4 = 10
> 1+2+3-4 = 2
> 1+2-3-4 = -4
> ....


Here's one way to do it--evaluating it would be a lot more complicated 
without eval(), which is our friend unless we are dealing with 
user-generated input.

for op1 in [:+, :-, :*, :/]
  for op2 in [:+, :-, :*, :/]
    for op3 in [:+, :-, :*, :/]
      expression = "1 #{op1} 2 #{op2} 3 #{op3} 4"
      puts "#{expression} = #{eval expression}"
    end
  end
end

Dan