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