# Random integer within a range?

I must create a little game; the one who play it must choose 2 numbers,
the beginning and the end of a range, and the program generate a secret
random number within that range, so the player must guess it!
But the problem is…how do I generate a random number?
I though at something like this:

number_to_guess = rand(n1…n2)

but it give me the error message “in `rand’: can’t convert Range into
Integer (TypeError)”

What can I do? Thanks!

Reiichi T.,

Is the range inclusive OR exclusive?

Should n1 OR n2 be reurned sometimes or never?

number_to_guess = rand(n1…n2)

David S. wrote:

Reiichi T.,

Is the range inclusive OR exclusive?

Should n1 OR n2 be reurned sometimes or never?

number_to_guess = rand(n1…n2)
Inclusive!

It’s work! Thank you David!
But there is no way to do it like in my version “rand(n1…n2)”? It’s
more friendly that way XD

Reiichi T. wrote:

Inclusive!

Okay, I’ll assume that these are two different positive integers.

Try this:

number_to_guess = (n2 > n1) ? n1 + rand((n2-n1+1)) : n2 +
rand((n1-n2+1))

On 01.03.2010 20:21, Reiichi T. wrote:

What can I do? Thanks!

rand only accepts an integer which will make it produce values in the
range 0…n (exclusive). So you can do:

irb(main):001:0> low, high = 12, 56
=> [12, 56]
irb(main):002:0> r = low + rand(high - low)
=> 54

Kind regards

robert

Reiichi T. wrote:

It’s work! Thank you David!
But there is no way to do it like in my version “rand(n1…n2)”? It’s
more friendly that way XD

#ruby 1.9
puts (10…20).to_a.sample
#ruby 1.8.6
puts (10…20).to_a.sort_by{rand}.pop

hth,

Siep

Reiichi T. wrote:

It’s work! Thank you David!
But there is no way to do it like in my version “rand(n1…n2)”? It’s
more friendly that way XD

Sure:

def myrand(r=nil)
if r.is_a?(Range)
rand(r.last - r.first + (r.exclude_end? ? 0 : 1)) + r.first
else
rand®
end
end

Or if you prefer:

module Kernel
alias :orig_rand :rand
def rand(r=nil)
if r.is_a?(Range)
orig_rand(r.last - r.first + (r.exclude_end? ? 0 : 1)) + r.first
else
orig_rand®
end
end
end

I suspect it’s not implemented in Ruby because it’s not obvious what
rand(0.3…5.7) should do.

On 01.03.2010 20:40, Reiichi T. wrote:

David S. wrote:

Reiichi T.,

Is the range inclusive OR exclusive?

Should n1 OR n2 be reurned sometimes or never?

number_to_guess = rand(n1…n2)
Inclusive!

Sorry, I answered before seeing this email. In that case it should be

irb(main):003:0> low, high = 12, 34
=> [12, 34]
irb(main):004:0> r = low + rand(high + 1 - low)
=> 22

You can also do something like this:

irb(main):012:0> (low…high).to_a.sample
=> 21
irb(main):013:0> (low…high).to_a.sample
=> 27

Although in that case you should store the array somewhere for
efficiency reasons.

Kind regards

robert

Under Ruby 1.9:

``````10.times.map{ Random.new.rand(20..30) } #=> [26, 26, 22, 20, 30,
``````

26, 23, 23, 25, 22]