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 arc4random" and still can't quite wrap my head around it. I've came up with some code but it's buggy.
float lowerBound = lowerBoundNumber.text.floatValue;
float upperBound = upperBoundNumber.text.floatValue;
float rndValue;
//if lower bound is lowerbound < higherbound else switch the two around before randomizing.
if(lowerBound < upperBound)
{
rndValue = (((float)arc4random()/0x100000000)*((upperBound-lowerBound)+lowerBound));
}
else
{
rndValue = (((float)arc4random()/0x100000000)*((lowerBound-upperBound)+upperBound));
}
Right now if I put in the values 0 and 3 it seems to work just fine. However if I use the numbers 10 and 15 I can still get values as low as 1.0000000 or 2.000000 for "rndValue".
Do I need to elaborate my algorithm or do I need to change the way I use arc4random?
You could simply use integer values like this:
int lowerBound = ...
int upperBound = ...
int rndValue = lowerBound + arc4random() % (upperBound - lowerBound);
Or if you mean you want to include float number between lowerBound and upperBound? If so please refer to this question: https://stackoverflow.com/a/4579457/1265516
The following code include the minimum AND MAXIMUM value as the random output number:
- (NSInteger)randomNumberBetween:(NSInteger)min maxNumber:(NSInteger)max
{
return min + arc4random_uniform((uint32_t)(max - min + 1));
}
Update:
I edited the answer by replacing arc4random() % upper_bound
with arc4random_uniform(upper_bound)
as @rmaddy suggested.
And here is the reference of arc4random_uniform for the details.
Update2:
I updated the answer by inserting a cast to uint32_t in arc4random_uniform()
as @bicycle indicated.
-(int) generateRandomNumberWithlowerBound:(int)lowerBound
upperBound:(int)upperBound
{
int rndValue = lowerBound + arc4random() % (upperBound - lowerBound);
return rndValue;
}
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.
Objective-C Function:
-(int)getRandomNumberBetween:(int)from to:(int)to
{
return (int)from + arc4random() % (to-from+1);
}
Swift:
func getRandomNumberBetween(_ from: Int, to: Int) -> Int
{
return Int(from) + arc4random() % (to - from + 1)
}
Call it anywhere by:
int OTP = [self getRandomNumberBetween:10 to:99];
NSLog(@"OTP IS %ld",(long)OTP);
NSLog(@"OTP IS %@",[NSString stringWithFormat @"%ld",(long)OTP]);
For Swift:
var OTP: Int = getRandomNumberBetween(10, to: 99)
In Swift:
let otp = Int(arc4random_uniform(6))
Try this.