Question

I want to create a simple calculator form in Rails 3.1 just for understanding. Via a form I want to get a number and multiplied it by two (for example).

I’ve created controller with index page (/index), then form in views:

<%= form_for @result do |f|%>
<%= f.label :number, 'Number' %>:
<%= f.text_field :number %>
<%= submit_tag 'Submit' %>
<%end%>
<%=@result%>

What I need to do with controller?

  def index
    @result = ''
  end
  def calculate
    @result = @number.to_i*2
  end

Answer 1

This is not gonna work. form_for is used to build forms for models that extend ActiveRecord. Use form_tag('/calculate') instead.

You need to define `match ‘calculate’ => ‘your_controller_name#calculate’ in config/routes.rb.

Additionally, you need a view for your calculate action – calculate.html.erb (you can call it differently but you’ll have to specify render 'view_name'.

Alternatively, if you want to use the same view file, use render :action => :index

Forgot to mention.
To access the data from the form, you use params[:key] hash.
So in your case it would look like @result = params[:number] * 2

This book is a great place to start with Rails.

Also, these screencasts are pretty helpful too