01202_simple-calc.mdown

simple-calc

simple-calc.png

# simple-calc.rb
class Calc              #1
  def initialize        #2
    @number = 0
    @previous = nil
    @op = nil
  end

  def to_s              #3
    @number.to_s
  end
  
  (0..9).each do |n|                              #4
    define_method "press_#{n}" do
      @number = @number.to_i * 10 + n
    end
  end

  def press_clear
    @number = 0
  end

  {'add' => '+', 'sub' => '-', 'times' => '*', 'div' => '/'}.each do |meth, op|   #5
    define_method "press_#{meth}" do
      if @op                                      #6
        press_equals
      end
      @op = op
      @previous, @number = @number, nil           #7
    end
  end

  def press_equals                                #8
    @number = @previous.send(@op, @number.to_i)
    @op = nil
  end

end

number_field = nil
number = Calc.new                                                 #9
Shoes.app :height => 250, :width => 200, :resizable => false do
  background "#EEC".."#996", :curve => 5, :margin => 2

  stack :margin => 2 do

    stack :margin => 8 do
      number_field = para strong(number)                          #10
    end

    flow :width => 218, :margin => 4 do
      %w(7 8 9 / 4 5 6 * 1 2 3 - 0 Clr = +).each do |btn|
        button btn, :width => 46, :height => 46 do                #11
          method = case btn
            when /[0-9]/: 'press_'+btn
            when 'Clr': 'press_clear'
            when '=': 'press_equals'
            when '+': 'press_add'
            when '-': 'press_sub'
            when '*': 'press_times'
            when '/': 'press_div'
          end
          
          number.send(method)                                     #12
          number_field.replace strong(number)                     #13
        end
      end
    end
  end

end

Study Note

#1:
Define a class Calc. This class has the following 18 methods.

• initialize
• to_s
• press_0, press_1, ..... , press_9
• press_clear
• press_add, press_sub, press_times, press_div
• press_equal

#2:
Define a method initialize. This method is used once in the above code to create just one object at #9.

#3:
Define a method to_s. In Shoes, para uses to_s implicitly at #10. If you comment out to_s definition lines, you will see the following output.

simple-calc-1.png

#4:
Define methods press_0, press_1, ..... , press_9 with the method define_method. See ri Module#define_method. They are the same as the following.

def press_0
  @number = @number.to_i * 10 + n
end
def press_1
  @number = @number.to_i * 10 + 1
end
         :
         : (and so on)

The .to_i is necessary for the case that @number is nil.

#5:
Define methods press_add, press_sub, press_times, press_div.

#6:
Execute the previous calculation (one of +, -, *, /).

#7:
To clear the number_field at #13 (to show nothing), assign nil to @number instead of 0.

#8:
Define a method press_equals. See the following small IRB snippet.

C:\>irb --simple-prompt
>> 23.send '+', 5
=> 28

#12:
Send the value (character string) that was assigned to the local variable method to the object number that was created at #9. See the following small IRB snippet.

C:\>irb --simple-prompt
>> class Calc
>>   def press_add
>>     puts 'DEBUG: hi.'
>>   end
>> end
=> nil
>> Calc.new.send 'press_add'
DEBUG: hi.
=> nil
>>

#13:
This line is defined within the button definition block (#11), hence every time when any button is clicked, number_field area will be refreshed.

Alternative Simple Calc

This is an alternative code. There is no interesting tips but it's simple, I guess. :)

#sample61.rb
Shoes.app :height => 250, :width => 200, :resizable => false do
  def do_calc
    @number = @previous.send(@op, @number)  if @op
    @op = nil
  end
  
  @previous, @number, @op = 0, 0, nil
  
  background "#EEC".."#996", :curve => 5, :margin => 2

  stack :margin => 2 do
    stack :margin => 8 do
      @number_field = para strong(@number)
    end

    flow :width => 218, :margin => 4 do
      %w(7 8 9 / 4 5 6 * 1 2 3 - 0 Clr = +).each do |btn|
        button btn, :width => 46, :height => 46 do
          case btn
            when /[0-9]/
              @number = @number.to_i * 10 + btn.to_i
            when 'Clr'
              @previous, @number, @op = 0, 0, nil
            when '='
              do_calc
            else
              do_calc
              @previous, @number = @number, nil
              @op = btn
          end      
          @number_field.replace strong @number
        end
      end
    end
  end
end