problem with a little ruby script

Question

i just began learning ruby. now im trying to code a little script which plays the montyhall problem i got a problem with the last line of the code

numgames = 10000 # Number of games to play 
switch = true # Switch your guess?
wins = 0
numgames.times do doors = [0, 0, 0] # Three doors! 
doors[rand(3)] = 1 # One of them has a car! 
guess = doors.delete_at(rand(3)) # We pick one of them!
doors.delete_at(doors[0] == 0 ? 0 : 1) # Take out one of the remaining doors that is not a car! 
wins += switch ? doors[0] : guess end
puts "You decided #{switch ? "" : "not "}to switch, and your win % is #{wins.times ()/numgames}"

miku · Accepted Answer · 2011-03-12 05:45:43Z

2

In the last line replace

wins.times ()

with

wins

times returns Enumerator, which doesn't play well with division.

edited Mar 12, 2011 at 5:45

answered Mar 12, 2011 at 5:15

miku

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4 Comments

Steve Addington Over a year ago

Thanks! But im still getting a syntax error. monty.rb:9: syntax error, unexpected ')' ...nd your win % is #{wins.size ()/numgames}"

miku Over a year ago

Are your parentheses balanced?

Steve Addington Over a year ago

Does that mean that every parantheses is correctly opened and closed? Then yes!

sarnold Over a year ago

wins is an integer. Why call times or size on an integer?

sarnold · Accepted Answer · 2011-03-12 05:37:23Z

1

Two problems:

First, wins and numgames are integers, and integer division returns an integer:

irb(main):001:0> 6632 / 10000
=> 0

So, change wins = 0 to wins = 0.0. This will force a floating point division, which will return a floating point answer.

Second, wins is a number, not an array. So get rid of wins.times() and wins.size(). Both are wrong.

With these two changes in place, I consistently get around 66% wins, which just goes to show that Marilyn vos Savant is way smarter than I am.

answered Mar 12, 2011 at 5:37

sarnold

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Comments

mu is too short · Accepted Answer · 2011-03-12 05:51:31Z

Your wins is an integer so you don't need .times or .size, you do, however, want .to_f to force things into floating point mode:

wins.to_f / numgames

And if you want a percentage, then you'll have to multiply by 100:

wins.to_f / numgames * 100

You should also properly indent your code for readability and break things up with line breaks to make it easier to read and easier for the parser to figure out:

numgames = 10000 # Number of games to play
switch = true # Switch your guess?
wins = 0
numgames.times do
    doors = [0, 0, 0] # Three doors!
    doors[rand(3)] = 1 # One of them has a car!
    guess = doors.delete_at(rand(3)) # We pick one of them!
    doors.delete_at(doors[0] == 0 ? 0 : 1) # Take out one of the remaining doors that is not a car!
    wins += switch ? doors[0] : guess
end
puts "You decided #{switch ? "" : "not "}to switch, and your win % is #{100 * wins.to_f / numgames}"

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