Newbie's need for help

ruby-talk
1

I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

2

There way to do it has been answered. The two main problems that I see here
are:

*Problem 1*
`Input1(new)` ...to create a new `Input1` object, you should call
`Input1.new` (i.e. call the new method on the Input1 class)

*Problem 2*
the `gets` method is returning a string, so you need to cast the variables
to integers somewhere (using .to_i) this can be in the class, or on gets
(i.e. `gets.to_i`)

···

On Sun, Aug 3, 2014 at 9:13 PM, Marc Chanliau <marc.chanliau@gmail.com> wrote:

I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

3

result = Input1.new( 10, 20 ).sum.to_s

= 30

?

···

On Mon, Aug 4, 2014 at 11:13 AM, Marc Chanliau <marc.chanliau@gmail.com> wrote:

I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

4

Thanks for the answer but that's not what I want to do. I want to use a
keyboard dialog where I prompt the use to enter two values separately. I
know how to write the script for that, I'm having problems with writing the
equivalent class.

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

Here is what happens when I run the class above:

~/desktop marcc$ ruby test1.rb

Enter first number:

12

Enter second number:

13

test1.rb:19:in `<main>': undefined local variable or method `new' for
main:Object (NameError)

···

On Sun, Aug 3, 2014 at 6:16 PM, Brett Herford-Fell <brettskiii@gmail.com> wrote:

result = Input1.new( 10, 20 ).sum.to_s

= 30

?

On Mon, Aug 4, 2014 at 11:13 AM, Marc Chanliau <marc.chanliau@gmail.com> > wrote:

I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

5

Marc,

You must first instantiate the class in order to access the instance
variables within the object. Here is what you could do. It isn't the best
way to write this code, but it should serve to help you understand how to
instantiate the class.

class Input1

  attr_accessor :n1, :n2

  def sum
    @n1 + @n2
  end

end

test_object = Input1.new

test_object.n1 = gets.chomp.to_i
test_object.n2 = gets.chomp.to_i

test_object.sum

Like I said, this isn't a beautiful example. However, in order to
access the instance variable held within the class, you need to set up
the attr_accessor.

If you have any questions about this, feel free to email me.

Phill

···

On Sun, Aug 3, 2014 at 9:16 PM, Brett Herford-Fell <brettskiii@gmail.com> wrote:

result = Input1.new( 10, 20 ).sum.to_s

= 30

?

On Mon, Aug 4, 2014 at 11:13 AM, Marc Chanliau <marc.chanliau@gmail.com> > wrote:

I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

6

Thanks for the answer.
In your example, however, there's no user interaction. I want to prompt the user to enter information as shown in my original code.
Marc

···

Sent from mobile device - Pardon possible typos!

On Aug 3, 2014, at 6:31 PM, Phillip Boone <phillipboone@gmail.com> wrote:

Marc,

You must first instantiate the class in order to access the instance variables within the object. Here is what you could do. It isn't the best way to write this code, but it should serve to help you understand how to instantiate the class.
class Input1

  attr_accessor :n1, :n2

  def sum
    @n1 + @n2
  end

end

test_object = Input1.new

test_object.n1 = gets.chomp.to_i
test_object.n2 = gets.chomp.to_i

test_object.sum

Like I said, this isn't a beautiful example. However, in order to access the instance variable held within the class, you need to set up the attr_accessor.

If you have any questions about this, feel free to email me.

Phill

On Sun, Aug 3, 2014 at 9:16 PM, Brett Herford-Fell <brettskiii@gmail.com> wrote:
result = Input1.new( 10, 20 ).sum.to_s

= 30

?

On Mon, Aug 4, 2014 at 11:13 AM, Marc Chanliau <marc.chanliau@gmail.com> wrote:
I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

7

Thanks for the answer, Jakub, that was very helpful.
Marc

···

Sent from mobile device - Pardon possible typos!

On Aug 3, 2014, at 6:40 PM, Jakub Subczynski <kubasub12@gmail.com> wrote:

There way to do it has been answered. The two main problems that I see here are:

Problem 1
`Input1(new)` ...to create a new `Input1` object, you should call `Input1.new` (i.e. call the new method on the Input1 class)

Problem 2
the `gets` method is returning a string, so you need to cast the variables to integers somewhere (using .to_i) this can be in the class, or on gets (i.e. `gets.to_i`)

On Sun, Aug 3, 2014 at 9:13 PM, Marc Chanliau <marc.chanliau@gmail.com> wrote:
I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

8

you don't pass new as a parameter, the following code works

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1.to_i + @n2.to_i
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts '--------------'
puts result = Input1.new(@n1, @n2).sum.to_s

➜ ruby git:(master) ✗ ruby test1.rb
Enter first number:
1
Enter second number:
2

···

--------------
3
➜ ruby git:(master) ✗

On Mon, Aug 4, 2014 at 11:31 AM, Phillip Boone <phillipboone@gmail.com> wrote:

Marc,

You must first instantiate the class in order to access the instance
variables within the object. Here is what you could do. It isn't the best
way to write this code, but it should serve to help you understand how to
instantiate the class.

class Input1

  attr_accessor :n1, :n2

  def sum
    @n1 + @n2
  end

end

test_object = Input1.new

test_object.n1 = gets.chomp.to_i
test_object.n2 = gets.chomp.to_i

test_object.sum

Like I said, this isn't a beautiful example. However, in order to access the instance variable held within the class, you need to set up the attr_accessor.

If you have any questions about this, feel free to email me.

Phill

On Sun, Aug 3, 2014 at 9:16 PM, Brett Herford-Fell <brettskiii@gmail.com> > wrote:

result = Input1.new( 10, 20 ).sum.to_s

= 30

?

On Mon, Aug 4, 2014 at 11:13 AM, Marc Chanliau <marc.chanliau@gmail.com> >> wrote:

I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

9

​Actually, there is user interaction -- it calls `gets` twice. It just
doesn't print anything. Surely you're capable of adding some `puts`es,
though.​

···

On 4 August 2014 15:09, Marc Chanliau <marc.chanliau@gmail.com> wrote:

Thanks for the answer.
In your example, however, there's no user interaction. I want to prompt
the user to enter information as shown in my original code.
Marc

10

common mistake I used to make always instationate a class and dont forget
your getter/setter method which in ruby is your _attr_aceessor it has the
getter setter both built in

···

On Sunday, August 3, 2014, Marc Chanliau <marc.chanliau@gmail.com> wrote:

Thanks for the answer but that's not what I want to do. I want to use a
keyboard dialog where I prompt the use to enter two values separately. I
know how to write the script for that, I'm having problems with writing the
equivalent class.

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

Here is what happens when I run the class above:

~/desktop marcc$ ruby test1.rb

Enter first number:

12

Enter second number:

13

test1.rb:19:in `<main>': undefined local variable or method `new' for
main:Object (NameError)

On Sun, Aug 3, 2014 at 6:16 PM, Brett Herford-Fell <brettskiii@gmail.com > <javascript:_e(%7B%7D,'cvml','brettskiii@gmail.com');>> wrote:

result = Input1.new( 10, 20 ).sum.to_s

= 30

?

On Mon, Aug 4, 2014 at 11:13 AM, Marc Chanliau <marc.chanliau@gmail.com >> <javascript:_e(%7B%7D,'cvml','marc.chanliau@gmail.com');>> wrote:

I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

11

Thanks for the answer, Brett, it helped a lot. Now I can see clearly what I was doing wrong.
Marc

···

Sent from mobile device - Pardon possible typos!

On Aug 3, 2014, at 6:34 PM, Brett Herford-Fell <brettskiii@gmail.com> wrote:

you don't pass new as a parameter, the following code works

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1.to_i + @n2.to_i
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts '--------------'
puts result = Input1.new(@n1, @n2).sum.to_s

➜ ruby git:(master) ✗ ruby test1.rb
Enter first number:
1
Enter second number:
2
--------------
3
➜ ruby git:(master) ✗

On Mon, Aug 4, 2014 at 11:31 AM, Phillip Boone <phillipboone@gmail.com> wrote:
Marc,

You must first instantiate the class in order to access the instance variables within the object. Here is what you could do. It isn't the best way to write this code, but it should serve to help you understand how to instantiate the class.
class Input1

  attr_accessor :n1, :n2

  def sum
    @n1 + @n2
  end

end

test_object = Input1.new

test_object.n1 = gets.chomp.to_i
test_object.n2 = gets.chomp.to_i

test_object.sum

Like I said, this isn't a beautiful example. However, in order to access the instance variable held within the class, you need to set up the attr_accessor.

If you have any questions about this, feel free to email me.

Phill

On Sun, Aug 3, 2014 at 9:16 PM, Brett Herford-Fell <brettskiii@gmail.com> wrote:

result = Input1.new( 10, 20 ).sum.to_s

= 30

?

On Mon, Aug 4, 2014 at 11:13 AM, Marc Chanliau <marc.chanliau@gmail.com> wrote:
I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

12

Yes, correct. I just realized that right after I sent my reply!
Thanks.

···

Sent from mobile device - Pardon possible typos!

On Aug 3, 2014, at 10:13 PM, Matthew Kerwin <matthew@kerwin.net.au> wrote:

On 4 August 2014 15:09, Marc Chanliau <marc.chanliau@gmail.com> wrote:

Thanks for the answer.
In your example, however, there's no user interaction. I want to prompt the user to enter information as shown in my original code.
Marc

​Actually, there is user interaction -- it calls `gets` twice. It just doesn't print anything. Surely you're capable of adding some `puts`es, though.​

13

In this example it may not make a difference but I would do the
conversion when the instance variables are set. Reason: then the data
members always have the proper type and you detect wrong values early
on. Also, it's more efficient in case someone is invoking #sum over
and over again. Thusly:

class Input1

  def initialize(n1, n2)
    @n1 = Integer(n1)
    @n2 = Integer(n2)
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
n1 = gets
puts "Enter second number: "
n2 = gets

puts Input1.new(n1, n2).sum
# or, more verbose and reusing your variable assignment
result = Input1.new(n1, n2).sum
puts result
# or holding on to the created instance of Input
data = Input1.new(n1, n2)
puts data.sum

Note: you do not need #to_s because puts does this implicitly.

I also fixed "problem" 3: using instance variables for input. This is
of course possible but a local variable seems more appropriate here.

Kind regards

robert

···

On Mon, Aug 4, 2014 at 7:15 AM, Marc Chanliau <marc.chanliau@gmail.com> wrote:

On Aug 3, 2014, at 6:40 PM, Jakub Subczynski <kubasub12@gmail.com> wrote:

There way to do it has been answered. The two main problems that I see here
are:

Problem 1
`Input1(new)` ...to create a new `Input1` object, you should call
`Input1.new` (i.e. call the new method on the Input1 class)

Problem 2
the `gets` method is returning a string, so you need to cast the variables
to integers somewhere (using .to_i) this can be in the class, or on gets
(i.e. `gets.to_i`)

--
[guy, jim].each {|him| remember.him do |as, often| as.you_can - without end}
http://blog.rubybestpractices.com/

14

Thanks. I'm practicing all the good advice I've had on this list.
Thanks!

···

On Sat, Aug 9, 2014 at 7:37 AM, James Goforth <jamgof08@gmail.com> wrote:

common mistake I used to make always instationate a class and dont forget
your getter/setter method which in ruby is your _attr_aceessor it has the
getter setter both built in

On Sunday, August 3, 2014, Marc Chanliau <marc.chanliau@gmail.com> wrote:

Thanks for the answer but that's not what I want to do. I want to use a
keyboard dialog where I prompt the use to enter two values separately. I
know how to write the script for that, I'm having problems with writing the
equivalent class.

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

Here is what happens when I run the class above:

~/desktop marcc$ ruby test1.rb

Enter first number:

12

Enter second number:

13

test1.rb:19:in `<main>': undefined local variable or method `new' for
main:Object (NameError)

On Sun, Aug 3, 2014 at 6:16 PM, Brett Herford-Fell <brettskiii@gmail.com> >> wrote:

result = Input1.new( 10, 20 ).sum.to_s

= 30

?

On Mon, Aug 4, 2014 at 11:13 AM, Marc Chanliau <marc.chanliau@gmail.com> >>> wrote:

I'm learning to write Ruby using classes (as opposed to scripts).
I can't get the following (extremely simple) class to run (although I
get the corresponding script right). What do I need to do to fix it?

Here is the class:

class Input1

  def initialize(n1, n2)
    @n1 = n1
    @n2 = n2
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
@n1 = gets
puts "Enter second number: "
@n2 = gets

puts result = Input1(new).sum.to_s

15

Thanks, Robert. I like the idea. It makes the class more general and the
instantiation cleaner.
Marc

···

On Mon, Aug 4, 2014 at 4:40 AM, Robert Klemme <shortcutter@googlemail.com> wrote:

On Mon, Aug 4, 2014 at 7:15 AM, Marc Chanliau <marc.chanliau@gmail.com> > wrote:

> On Aug 3, 2014, at 6:40 PM, Jakub Subczynski <kubasub12@gmail.com> > wrote:
>
> There way to do it has been answered. The two main problems that I see
here
> are:
>
> Problem 1
> `Input1(new)` ...to create a new `Input1` object, you should call
> `Input1.new` (i.e. call the new method on the Input1 class)
>
> Problem 2
> the `gets` method is returning a string, so you need to cast the
variables
> to integers somewhere (using .to_i) this can be in the class, or on gets
> (i.e. `gets.to_i`)

In this example it may not make a difference but I would do the
conversion when the instance variables are set. Reason: then the data
members always have the proper type and you detect wrong values early
on. Also, it's more efficient in case someone is invoking #sum over
and over again. Thusly:

class Input1

  def initialize(n1, n2)
    @n1 = Integer(n1)
    @n2 = Integer(n2)
  end

  def sum
    @n1 + @n2
  end

end

puts "Enter first number: "
n1 = gets
puts "Enter second number: "
n2 = gets

puts Input1.new(n1, n2).sum
# or, more verbose and reusing your variable assignment
result = Input1.new(n1, n2).sum
puts result
# or holding on to the created instance of Input
data = Input1.new(n1, n2)
puts data.sum

Note: you do not need #to_s because puts does this implicitly.

I also fixed "problem" 3: using instance variables for input. This is
of course possible but a local variable seems more appropriate here.

Kind regards

robert

--
[guy, jim].each {|him| remember.him do |as, often| as.you_can - without
end}
http://blog.rubybestpractices.com/

16

Have fun learning Ruby! Your question was answered but I hope this
helps understand the context too:
http://codelikethis.com/lessons/ruby_objects/classes

···

On Mon, Aug 4, 2014 at 12:02 PM, Marc Chanliau <marc.chanliau@gmail.com> wrote:

Thanks, Robert. I like the idea. It makes the class more general and the
instantiation cleaner.

--
Alex Chaffee - alex@stinky.com
http://alexchaffee.com
http://codelikethis.com
http://twitter.com/alexch

17

Thanks, Alex.
Interesting and concise. Good learning tool.

···

Sent from mobile device - Pardon possible typos!

On Aug 4, 2014, at 2:54 PM, Alex Chaffee <alex@stinky.com> wrote:

On Mon, Aug 4, 2014 at 12:02 PM, Marc Chanliau <marc.chanliau@gmail.com> wrote:
Thanks, Robert. I like the idea. It makes the class more general and the
instantiation cleaner.

Have fun learning Ruby! Your question was answered but I hope this
helps understand the context too:
http://codelikethis.com/lessons/ruby_objects/classes

--
Alex Chaffee - alex@stinky.com
http://alexchaffee.com
http://codelikethis.com
http://twitter.com/alexch