Swift convert UInt to Int

Question

I have this expression which returns a UInt32:

let randomLetterNumber = arc4random()%26

I want to be able to use the number in this if statement:

if letters.count > randomLetterNumber{
    var randomLetter = letters[randomLetterNumber]
}

This issue is that the console is giving me this

Playground execution failed: error: <REPL>:11:18: error: could not find an overload for '>' that accepts the supplied arguments
if letters.count > randomLetterNumber{
   ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~

The problem is that UInt32 cannot be compared to an Int. I want to cast randomLetterNumber to an Int. I have tried:

let randomLetterUNumber : Int = arc4random()%26
let randomLetterUNumber = arc4random()%26 as Int

These both cause could not find an overload for '%' that accepts the supplied arguments.

How can I cast the value or use it in the if statement?

Solution 1

Int(arc4random_uniform(26)) does two things, one it eliminates the negative results from your current method and second should correctly creat an Int from the result.

Solution 2

More simple than this, impossible:

Int(myUInteger)

Solution 3

Just create a new int with it

let newRandom: Int = Int(randomLetterNumber)
if letters.count > newRandom {
    var randomLetter = letters[newRandom]
}

or if you never care about the UInt32 you can just create an Int immediately:

let randomLetterNumber = Int(arc4random() % 26)

Solution 4

You can do

let u: UInt32 = 0x1234abcd
let s: Int32 = Int32(bitPattern: u)

View more solutions

Comments

[David Berry]

Note that this will throw an exception half the time due to overflow checking, use the answer I gave to avoid that.

[67cherries]

Thanks for that, the Int() initializer seems to do the trick.

[Firo]

@David, how so? Not disagreeing, just want to understand what you mean.

[Nate Cook]

You can read more about numeric type conversion in Apple's Swift docs.

[David Berry]

Actually it won't since you're doing the casting after the modulo, so you can guarantee it's always in bounds. Int(arc4random()) will crash 50% of the time it's executed on a 32-bit platform because a UInt32 won't fit in an Int32. Just seen too many "arc4random is bugged and crashes" questions with swift. In any case arc4random_uniform will give a more uniform distribution.

[nacross]

Thanks. I had a similar problem with arc4random_uniform(someArray.count) casting fixes the problem arc4random_uniform(UInt32(someArray.count))

[cbowns]

Modifying/bounding the output of a random number distribution with modulo or division operations is poor form: it ruins the distribution properties that the functions guarantee. Instead, use arc4random_uniform(26) to let the function uphold a uniform distribution across the range you specify.

[bshirley]

I had both problems: probability = Int(arc4random_uniform(UInt32(total))) … the main problem is because of the headers the type-ahead doesn't have info on this method and doesn't provide the needed metadata (which it would then offer as suggestions to fix the problem)

[0xKayvan]

This does the exact opposite of what OP asked. Should be Int(myUInteger)

[João Serra]

this suddenly start giving me "Not enough bits to represent the passed value" more specifically Int(arc4random())