CODEWITHSUNDEEP
ruby
Aleks
Aleks

Reputation: 5320

Why does the rand() return always the same number?

I am using

rand(200)

in my Rails application. When I run it in console it always returns random number, but if I use it in application line:

index = rand(200)

index is always the same number.

Why is that and how to overcome this?

Upvotes: 0

Views: 1807

Answers (3)

matt
matt

Reputation: 535121

Simple pseudo-random number generators actually generate a fixed sequence of numbers. The particular sequence you get is determined by the initial "seed" value. My suspicion is that you are always getting the first number in the same sequence. Therefore I suggest we try to change the sequence by calling srand every time before calling rand, thus changing the seed value every time. The docs explain that, when called without a parameter, srand generates a new seed based on current circumstances (e.g. the time on the clock). Thus you should get a difference sequence and hence a different random number:

srand
rand(200)

Now, you may ask - why are you always getting the same sequence? I have no idea! As someone else suggested in one of the comments, the behavior you are seeing is the behavior one would expect if you had other code, anywhere, that calls srand with the same, fixed value every time. So it might be good to look for that.

Upvotes: 4

Jason R
Jason R

Reputation: 2145

Try Random.rand(). For example

Random.rand(200)

Or if you're working with an array you could use sample.

[*1..200].sample

Upvotes: 0

PhillipKregg
PhillipKregg

Reputation: 9358

rand(200) is run once and that value is assigned to your index variable. So 'index' will always be that number.

If you want index to change, you will need to continually run rand on it.

Here's a simple way to do that:

def randomIndex(num)
  index = rand(num)
  return index
end

randomIndex(200)
=> // this value will change

Upvotes: -1

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