Initial stages of scripting

Hi there,
I’m a relative newbie when it comes to scripting in ruby however, for a
year 11 project at school, it is necesary for me to program a maths
utilit which requests a user - elementary school aged - to add to
numbers together to reach an answer. I’ve effected some coding however,
I’m a little stumpt as to why the aplet is not correctly parsing through
the loops.
===script extract starts==
question = 1
unless question == 20
score = 0
number_of_questions = 0
num1 = rand(20)
num2 = rand(20)
correct_answer = num1 + num2
puts(“What is #{num1} + #{num2}/?”)
user_answer = gets.chomp!.to_i
unless user_answer == correct_answer
puts(“Sorry, that is not correct. Please try again.”)
user_answer = gets.chomp!.to_i
end
score += 1
number_of_questions += 1
question += 1
puts(“Well done! That is correct.\nYou have answered #{score} out of
#{number_of_questions} questions correctly.”)
end
exit
===script extract ends===
Cheers,
Hayden

On Thu, 2008-05-08 at 19:27 +0900, Hayden Smith wrote:

puts(“What is #{num1} + #{num2}/?”)
exit
===script extract ends===

What loops? I don’t see any loops in there at all. I see two
conditionals (“unless question == 20” and “unless user_answer ==
correct_answer”) but no loops.

That might be a clue.

I dont want to go through it all, so just a few hints:

puts(“What is #{num1} + #{num2}/?”)

No need for the () here.
Also the / before the ? seems confusing. Maybe omit it.

The
exit
also seems superfluous. Maybe omit it.

My favourite loop in ruby is this:

loop {

do something here… alter condition, and then finally

break if condition
}

But maybe you meant to use a while
I personally think “until” is not a good name for use here.

On 8 May 2008, at 11:27, Hayden Smith wrote:

score = 0
score += 1
number_of_questions += 1
question += 1
puts(“Well done! That is correct.\nYou have answered #{score} out of
#{number_of_questions} questions correctly.”)
end
exit

Hi Hayden,

I hope the following answers are helpful. The idiom that you’d be
looking to use in your code would be:

score = 0
1…20.each do |question|
# do stuff
end

where you keep track of the score yourself as part of do stuff.
Although I prefer the form:

1…20.inject(0) |sum, question|
# do stuff
sum += some_condition ? 1 : 0
end

but that requires that the last expression in the block be the one
that increments the sum variable. Extra marks if you can write the
block without using any local variables :wink:

Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net

raise ArgumentError unless @reality.responds_to? :reason

On 8 May 2008, at 12:07, Eleanor McHugh wrote:

1…20.inject(0) |sum, question|
# do stuff
sum += some_condition ? 1 : 0
end

which of course should be:

1…20.inject(0) |sum, question|
#do stuff
sum + (some_condition ? 1 : 0)
end

as the whole point of inject is that it does the assignment for you…
I really must stick to this rule of no coding before my second cup of
tea of the day :wink:

Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net

raise ArgumentError unless @reality.responds_to? :reason

My apologies for misuse of terminology: Those two conditionals are the
particular elements that I speak of.
----- Original Message -----
From: Michael T. Richter
To: ruby-talk ML
Sent: Thursday, May 08, 2008 8:41 PM
Subject: Re: initial stages of scripting

On Thu, 2008-05-08 at 19:27 +0900, Hayden Smith wrote:
Hi there,
I’m a relative newbie when it comes to scripting in ruby however, for a
year 11 project at school, it is necesary for me to program a maths
utilit which requests a user - elementary school aged - to add to
numbers together to reach an answer. I’ve effected some coding however,
I’m a little stumpt as to why the aplet is not correctly parsing through
the loops.
===script extract starts==
question = 1
unless question == 20
score = 0
number_of_questions = 0
num1 = rand(20)
num2 = rand(20)
correct_answer = num1 + num2
puts(“What is #{num1} + #{num2}/?”)
user_answer = gets.chomp!.to_i
unless user_answer == correct_answer
puts(“Sorry, that is not correct. Please try again.”)
user_answer = gets.chomp!.to_i
end
score += 1
number_of_questions += 1
question += 1
puts(“Well done! That is correct.\nYou have answered #{score} out of
#{number_of_questions} questions correctly.”)
end
exit
===script extract ends===

What loops? I don’t see any loops in there at all. I see two
conditionals (“unless question == 20” and “unless user_answer ==
correct_answer”) but no loops.

That might be a clue.

    --
    Michael T. Richter <[email protected]> (GoogleTalk: 

[email protected])
The only reason some people get lost in thought is because it’s
unfamiliar territory. (Paul Fix)

Hi Ellie,
Thanks for the suggestions, but as is evident from this code - I believe

  • I
    am a relative newbie and therefore, the logic behind this - at this
    point -
    is beyond me. Oh well, back to the bottom of the class for me.
    Cheers
    ----- Original Message -----
    From: “Eleanor McHugh” [email protected]
    To: “ruby-talk ML” [email protected]
    Sent: Thursday, May 08, 2008 9:07 PM
    Subject: Re: initial stages of scripting

Hi,
If I were to pursue this line of logic, how would I allow the break to
have
two conditions to opperate on? For example, in my first nested loop, I
wished to test for the equality of user_answer and correct_answer as
well
as - this was not included due to my ignorance - a comparison to only
continue the loop - regardless whether the two previous were correct -
but
only whilst looper != 3.
Cheers,
Hayden
----- Original Message -----
From: “Marc H.” [email protected]
Newsgroups: comp.lang.ruby
To: “ruby-talk ML” [email protected]
Sent: Thursday, May 08, 2008 8:48 PM
Subject: Re: initial stages of scripting

On 8 May 2008, at 12:36, Hayden Smith wrote:

Hi Ellie,
Thanks for the suggestions, but as is evident from this code - I
believe - I am a relative newbie and therefore, the logic behind
this - at this point - is beyond me. Oh well, back to the bottom of
the class for me.
Cheers

Well I didn’t want to ruin your homework assignment for you so I sort
of dodged around your actual task. Apologies if the following breaks
that rule, but getting the hang of basic loops etc. is a fundamental
if you want to really enjoy programming.

If I lay out your code to better reflect the logical structure it
looks like this:

question = 1
unless question == 20
  score = 0
  number_of_questions = 0
  num1 = rand(20)
  num2 = rand(20)
  correct_answer = num1 + num2
  puts("What is #{num1} + #{num2}/?")
  user_answer = gets.chomp!.to_i
end
score += 1
number_of_questions += 1
question += 1
puts("Well done! That is correct.\nYou have answered #{score} out of

#{number_of_questions} questions correctly.")
end
exit

Clearly there’s either a fragment missing at the very start which
would matches with the final ‘end’ statement, or else your first ‘end’
statement is an erroneous inclusion. This is one of the reasons for
laying out code with clear indentation - it makes the logic flow
glaringly obvious.

It would make sense to put some kind of loop statement at the start
otherwise there will be no repetition. With this inclusion what you
have is a classic example of what’s known as a sentinel guarded loop.
You have a sentinel value (in this case 20) and an accumulator
‘question’ which changes value with each loop iteration until it
reaches a specified value. The way in which you would handle this in a
traditional procedural language such as BASIC would be to write a code
fragment of this form:

FOR QUESTION = 1 TO 20
num1 = RND(20)
num2 = RND(20)
correct_answer = num1 + num2
REM read the value from the keyboard
REM compare the result and do some stuff
REM etc.
END

In Ruby it’s more natural for these kinds of problems to use a Range
object (because Ruby is object-oriented) and then enumerate across it:

questions = 1…20 # this creates an instance of the Range 1 through
20
questions.each do |question|
# actions to do for the question asked
end

but you can also use a more procedural style:

questions = 1…20 # this creates an instance of the Range 1 through
20
for question in questions
# actions to do for the question asked
end

and either form would provide the loop that you need to ask the user
for their answer to successive questions.

If you then study the actions that you’re taking in your code and
consider the actual logic of what you’re trying to achieve you’ll
notice that the score generated will be incorrect. This is where my
suggestion of enumerating a Range object using the inject() method
rather that each() becomes relevant:

questions = 1…20 # this creates an instance of the Range 1 through
20
questions.inject(0) do |sum, question|
#do stuff
sum + (some_condition ? 1 : 0)
end

The ‘sum’ parameter to the block acts as an accumulator and for each
element in the range ‘questions’ whatever the final expression of the
code block evaluates to will be the value stored in ‘sum’. Once all
elements have been enumerated, the value in ‘sum’ is then returned by
inject() as the value of the expression. So for example:

numbers = 1…20
result = numbers.inject(0) do |sum, number|
sum + number
end

would set ‘result’ to 210, which is the sum of the first twenty
integers. The way in which this then applies to your problem:

questions = 1…20 # this creates an instance of the Range 1 through
20
correct_answers = questions.inject(0) do |sum, question|
#do stuff
sum + (condition_for_correct_answer ? 1 : 0)
end

The use of the ternary logic operator is compact but for more complex
behaviour a clearer formulation would be:

correct_answers = questions.inject(0) do |sum, question|
#do stuff
sum + if condition_for_correct_answer ? then
# print some stuff
1
else
# print some other stuff
0
end
end

which takes advantage of the fact that ‘if’ is also an expression and
will return a value which can be used directly. In languages where
‘if’ is a statement (and hence does not return a value itself) the
logic would look more like:

correct_answers = 0
questions.each do |question|
#do stuff
if condition_for_correct_answer ? then
# print some stuff
correct_answers += 1
else
# print some other stuff
correct_answers += 0
end
end

which is also valid Ruby.

And if that’s not baffled you completely, you’ll be well on your way
to Ruby mastery :slight_smile:

Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net

raise ArgumentError unless @reality.responds_to? :reason

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