Cannot convert value of type 'Int' to expected argument type 'UInt32'

Question

I am trying to generate a random number in Swift:

var amountOfQuestions = 2
var randomNumber = Int(arc4random_uniform(amountOfQuestions - 1)) + 1

but this results in the error:

Cannot convert value of type 'Int' to expected argument type 'UInt32'

What is the problem? Any ideas on what I can do to fix this error?

Haas

Did you try casting (amountOfQuestions - 1) to UInt32? – Citrate

Answer 1

Make your amountOfQuestions variable an UInt32 rather than an Int inferred by the compiler.

var amountOfQuestions: UInt32 = 2

// ...

var randomNumber = Int(arc4random_uniform(amountOfQuestions - 1)) + 1

arc4random_uniform requires a UInt32.

From the Darwin docs:

arc4random_uniform(u_int32_t upper_bound);

Burushaski

Furthermore, it's worth noting that if amountOfQuestions is computed, for instance from the size of an array, the appropriate answer might just be to cast it to UInt32 using the constructor, ie., UInt32(questions.count). – Baffle

Answer 2

Declare amountOfQuestions as a UInt32:

var amountOfQuestions: UInt32 = 2

PS: If you want to be grammatically correct it's number of questions.

Citrate

Answer 3

First thing: The method "arc4random_uniform" expects an argument of type UInt32, so when you put that subtraction there, it converted the '1' you wrote to UInt32.

Second thing: In swift you can't subtract a UInt32 (the '1' in your formula) from an Int (in this case 'amountOfQuestions').

To solve it all, you'll have to consider changing the declaration of 'amountOfQuestions' to:

var amountOfQuestions = UInt32(2)

That should do the trick :)

Pharyngitis

Your second part, while partially true (it's true that you can't subtract a UInt32 from an Int), is irrelevant. In this case the 1 will automatically be the appropriate type, in this case an Int to match amountOfQuestions for the subtraction to work. The problem is that that Int can't be passed to arc4random_uniform, which expects a UInt32 argument. Note that it's perfectly valid to use UInt32(2) - 1 and the result is also a UInt32 (which is why your actual fix works) – Baffle

The second part was used to complete the thought. In the code presented by the question, amountOfQuestions wasn't an UInt32. There was only one solution in my answer, I just broke in two for him to understand it better. What you said about being perfect valid to UInt32 is known and totally irrelevant too.... – Pharyngitis