Fizz Buzz in Swift

Published on 03 October 2018 (Updated: 28 April 2022)

Welcome to the Fizz Buzz in Swift page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

func fizzBuzz(start: Int = 1, end: Int = 100) -> Void {
    let range = start...end
    for number in range {
        guard number % 5 == 0 || number % 3 == 0 else {
        var fizzAndOrBuzz = ""
        if number % 3 == 0 {
            fizzAndOrBuzz = "Fizz"
        if number % 5 == 0 {
            fizzAndOrBuzz += "Buzz"


Fizz Buzz in Swift was written by:

This article was written by:

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

The Function Signature

Here we see a rather long and punctuation-filled function signature. Swift functions use named parameters, and the type of each parameter must be noted. This is a safety feature, ensuring, for example, that we don't pass in a float when we need an integer. So, in line 1, we see start: Int and end: Int, meaning that our function takes in two integer values, named start and end.

Default Values

You might think that the equal signs next to each parameter look like assignments, and you would be (sort of) correct. When writing a Swift function's signature, the equals sign can be used to define a default value. If later, the user chooses to call the function without passing in any arguments, the compiler will be smart enough to look at the defaults, and run the function using those values. Swift functions don't need to have default values, but they can be nice to have. They can save you some headaches when building apps.

The Return Type

The little arrow after the argument names indicates the return type, which in this case is Void. Void just means our function doesn't return anything. Our function is only printing out words and numbers, so it isn't returning any values.

In Swift, if you function doesn't return anything, you can leave off the return type completely, or use the empty tuple () to indicate Void. However, I think it's best to just be explicit about what you're returning and write it out.


On line 2, we use the keyword let to define a new range of numbers:

let range = start...end

In Swift, values defined with let are immutable, and we are encouraged to use them liberally. This keeps us from accidentally changing something when we don't want or need to.

Ranges are their own type in Swift, and allow us to go over a series of numbers without setting up a list or array. Although we could have explicitly named the type here, the Swift compiler is able to infer that we want a range because we've given it two integer values, separated by an ellipsis.

We create a for-loop to transverse the range on line 4. Earlier versions of Swift allowed for C-style loops, but they've since been replaced with this less wordy syntax.


Line 5 presents a guard statement, a kind of conditional that only fires if a condition has not been met. Guard statements are frequently used in Swift to handle edge cases that might otherwise cause errors, and to avoid nested conditionals. Here, we use a guard statement to swiftly print any numbers that are not divisible by 3 or 5. Then, we continue on to the next number.

If a number is indeed divisible by 3 or 5, we set up the variable fizzAndOrBuzz. This value is defined with the keyword var, which allows us to change it over the course of our function.

We use two if-statements to test for Fizziness and/or Buzziness. Both statements use the remainder operator, %, which gives us the remainder from any division between one integer and another. If one number is evenly divisible by another, the remainder is always 0.

In other languages, % is used for the modulo operator. Modulo is similar to remainder when dealing with positive integers, but it gives different results when the integers are negative. In Swift, the absolute values of the integers are used, so 3 % 15 gives the same result as 3 % -15.

Wrapping Up

Line 14 uses += to add "Buzz" on to the end of our variable, so that if our number is evenly divisible by both 3 and 5, we get the word "FizzBuzz", and not just "Fizz" or just "Buzz".

Finally, we print whatever is inside fizzAndOrBuzz at the end of our loop.

We exit the loop, we end the function, and we call fizzBuzz at the very bottom. Since we've defined some default values, the script knows to go over the numbers 1 through 100 without having to be told to. We could also pass in arguments for the start and end of our range later, if we want.

How to Run the Solution

Swift is often run via XCode, Apple's IDE, or by installing Swift on Linux. However, XCode in particular is a heavy download, so unless you already have it installed, or are seriously contemplating iOS development, you probably should use this handy online Swift compiler.

Please be aware that Swift updates very frequently, and many online compilers use earlier versions of the language, which may present with incompatibilities and errors when trying to run this code. This code was written in Swift 4.