Generate Random Numbers Between Two Numbers in Objective-C

Question

I have two text boxes and user can input 2 positive integers (Using Objective-C). The goal is to return a random value between the two numbers.

I\'ve used \"man arc4

Answer 1

You should avoid clamping values with mod (%) if you can, because even if the pseudo-random number generator you're using (like arc4random) is good at providing uniformly distributed numbers in its full range, it may not provide uniformly distributed numbers within the restricted modulo range.

You also don't need to use a literal like 0x100000000 because there is a convenient constant available in stdint.h:

(float)arc4random() / UINT32_MAX

That will give you a random float in the interval [0,1]. Note that arc4random returns an integer in the interval [0, 2**32 - 1].

To move this into the interval you want, you just add your minimum value and multiply the random float by the size of your range:

lowerBound + ((float)arc4random() / UINT32_MAX) * (upperBound - lowerBound);

In the code you posted you're multiplying the random float by the whole mess (lowerBound + (upperBound - lowerBound)), which is actually just equal to upperBound. And that's why you're still getting results less than your intended lower bound.