The params hash contains all the url and post parameters that were passed to your application.
You can access it from inside any controller, like so:
Say you have defined a route like so:
get '/hello/:hello/:everyone' => 'hello#index', :as => :hello_world
In your controller, you can access:
These will automatically be extracted from the route.
Exercise - Make a calculator
We are going to make a simple calculator, you will be able to give it two numbers, and have it give you the sum.
First create a controller and route. The routes should have space for two numbers. It should be possible to hit a URL like this:
Retrieve the values and store in instance variables
Now in your controller, retrieve these from the params hash and store them in instance variables, @number_1 and @number_2
Sum them in the view
Finally create a view. In the view, sum together the two numbers, giving a nice output.
Try and think of a way you can make this work using a form. You will need to change the route to accomplish this.