# How do I get a random number between two random numbers?

Discussion in 'Ruby' started by Alex Untitled, Nov 15, 2009.

1. ### Alex UntitledGuest

I want to create a program that asks you to guess a number between two
numbers. The problem is that I can't figure out how to make the numbers
that you're guessing between random and have the random number you are
guessing between those two numbers. Does anybody know how to do this?
--
Posted via http://www.ruby-forum.com/.

Alex Untitled, Nov 15, 2009

2. ### Marnen Laibow-KoserGuest

Alex Untitled wrote:
> I want to create a program that asks you to guess a number between two
> numbers. The problem is that I can't figure out how to make the numbers
> that you're guessing between random and have the random number you are
> guessing between those two numbers. Does anybody know how to do this?

Well, you know how to generate the first two random numbers, right?
Just take the difference between those two as the range in which to
generate the third. Simple.

Best,
--
Marnen Laibow-Koser
http://www.marnen.org

--
Posted via http://www.ruby-forum.com/.

Marnen Laibow-Koser, Nov 15, 2009

3. ### Alex UntitledGuest

Marnen Laibow-Koser wrote:
> Alex Untitled wrote:
>> I want to create a program that asks you to guess a number between two
>> numbers. The problem is that I can't figure out how to make the numbers
>> that you're guessing between random and have the random number you are
>> guessing between those two numbers. Does anybody know how to do this?

>
> Well, you know how to generate the first two random numbers, right?
> Just take the difference between those two as the range in which to
> generate the third. Simple.
>
> Best,
> --
> Marnen Laibow-Koser
> http://www.marnen.org
>

So, would it be something like this?

num1 = rand(101)
num2 = rand(101)
num3 = num1 + num2

Anyway, thank you!
--
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Alex Untitled, Nov 15, 2009
4. ### Tony ArcieriGuest

[Note: parts of this message were removed to make it a legal post.]

On Sat, Nov 14, 2009 at 7:54 PM, Alex Untitled <>wrote:

> I want to create a program that asks you to guess a number between two
> numbers. The problem is that I can't figure out how to make the numbers
> that you're guessing between random and have the random number you are
> guessing between those two numbers. Does anybody know how to do this?
>

first + rand(last + 1 - first)

--
Tony Arcieri
Medioh/Nagravision

Tony Arcieri, Nov 15, 2009
5. ### Alex UntitledGuest

OK, that didn't work. That just added the two numbers. How do I make a
number between two numbers again? I can't seem to find it.
--
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Alex Untitled, Nov 15, 2009
6. ### Alex UntitledGuest

Alex Untitled wrote:
> OK, that didn't work. That just added the two numbers. How do I make a
> number between two numbers again? I can't seem to find it.

--
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Alex Untitled, Nov 15, 2009
7. ### Alex UntitledGuest

I found the solution.

num1 = rand(1001)
num2 = 1001 + rand(1001)
number = num1 + rand(num2)
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Alex Untitled, Nov 15, 2009
8. ### Steve WilhelmGuest

Alex Untitled wrote:
> I found the solution.
>
> num1 = rand(1001)
> num2 = 1001 + rand(1001)
> number = num1 + rand(num2)

This can return: num1 = 1000, num2 = 1001, number = 2001

Try

module RandomNumberBetweenTwoRandomNumbers
def self.generate max
first = 1 + rand(max - 2);
second = max - rand(max - (first + 1))
between = first + 1 + rand((second - first) - 1)
[first, between, second]
end
end

puts RandomNumberBetweenTwoRandomNumbers::generate 10
puts RandomNumberBetweenTwoRandomNumbers::generate 100
puts RandomNumberBetweenTwoRandomNumbers::generate 1000

--
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Steve Wilhelm, Nov 16, 2009
9. ### Josh CheekGuest

[Note: parts of this message were removed to make it a legal post.]

On Sat, Nov 14, 2009 at 8:54 PM, Alex Untitled <>wrote:

> I want to create a program that asks you to guess a number between two
> numbers. The problem is that I can't figure out how to make the numbers
> that you're guessing between random and have the random number you are
> guessing between those two numbers. Does anybody know how to do this?
> --
> Posted via http://www.ruby-forum.com/.
>
>

max = 100

low , high = [ rand(max) , rand(max) ].sort

difference = high - low

middle = low + rand(difference).to_i #to_i for if low and high have same
value

puts "low = #{low}"
puts "middle = #{middle}"
puts "high = #{high}"

Josh Cheek, Nov 16, 2009
10. ### Steve WilhelmGuest

Josh Cheek wrote:

>
> # How about something like:
>
> max = 100
>
> low , high = [ rand(max) , rand(max) ].sort
>
> difference = high - low
>
> middle = low + rand(difference).to_i #to_i for if low and high have
> same
> value
>
> puts "low = #{low}"
> puts "middle = #{middle}"
> puts "high = #{high}"

The problem with your solution is that low and high can be the same
number.
--
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Steve Wilhelm, Nov 16, 2009
11. ### Josh CheekGuest

[Note: parts of this message were removed to make it a legal post.]

On Mon, Nov 16, 2009 at 1:45 AM, Steve Wilhelm <> wrote:

> Josh Cheek wrote:
>
> >
> > # How about something like:
> >
> > max = 100
> >
> > low , high = [ rand(max) , rand(max) ].sort
> >
> > difference = high - low
> >
> > middle = low + rand(difference).to_i #to_i for if low and high have
> > same
> > value
> >
> > puts "low = #{low}"
> > puts "middle = #{middle}"
> > puts "high = #{high}"

>
> The problem with your solution is that low and high can be the same
> number.
> --
> Posted via http://www.ruby-forum.com/.
>
>

In that case, the cardinality of the solution set is 1, perhaps not
desirable for a guessing game, but it is not stated that this should not
happen, and if no minimum range is specified, then it is subjective where
that line is drawn. ie if a solution set with cardinality 1 is not
appropriate, then what about a solution set with cardinality two? At what
point do we say the numbers are sufficiently far apart that they are
acceptable?

Perhaps a different approach is required altogether. Instead of giving the
maximum value the numbers can be, give the minimum and maximum difference
between the numbers. I don't see much value in a minimum number anyway,
choosing a random number between 90 and 100 doesn't seem to offer anything
over choosing a minimum number between 0 and 10.

While I think saying "give me an upper bound between 10 and 20, with a
target between 0 and that number" is a better approach, it is not what was
than to impose my own restrictions.

Josh Cheek, Nov 16, 2009
12. ### Giampiero ZanchiGuest

ciao
a lot of improvements is possible;

range_size = 64
n_middle = rand(101) + range_size
n_decrease = rand(range_size)
n_left = n_middle - n_decrease
n_right = n_middle + (range_size - n_decrease - 1)
p "#{n_left} - #{n_middle} - #{n_right}"
--
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Giampiero Zanchi, Nov 16, 2009