This tutorial belongs to the Swift series

if is the most common way to make a decision in code. You write the if keyword, a boolean expression, and a block of code that runs only when the expression is true:

let condition = true
if condition == true {
    // code executed if the condition is true
}

Add an else block to run something when the condition is false:

let condition = true
if condition == true {
    // code executed if the condition is true
} else {
    // code executed if the condition is false
}

Writing the condition

You can wrap the condition in parentheses if you like the look:

if (condition == true) {
    // ...
}

Swift doesn’t need them, and most Swift code leaves them out. And since condition is already a Bool, comparing it to true adds nothing. You can write:

if condition {
    // runs if `condition` is `true`
}

or negate it with !:

if !condition {
    // runs if `condition` is `false`
}

A realistic example

Here’s how it looks with a real value:

let age = 17

if age >= 18 {
    print("You can vote")
} else {
    print("Not yet")
}

This prints Not yet.

Chaining with else if

When there are more than two outcomes, chain conditions with else if:

let temperature = 34

if temperature < 12 {
    print("Bring a jacket")
} else if temperature > 30 {
    print("Stay hydrated")
} else {
    print("Nice weather")
}

Swift checks the conditions from top to bottom and runs the first block whose condition is true. Then it skips the rest. Here it prints Stay hydrated.

If a chain grows past three or four branches, a switch is usually cleaner. That’s the next lesson.

The condition must be a Bool

In Swift the condition must be an actual Bool. You can’t write if count with a number, like you would in JavaScript. Write if count > 0 instead. It’s a few more characters, and it removes any doubt about what you’re checking.

No assignment in a condition

One thing that separates Swift from many other languages: it prevents the classic bug of typing = (assignment) when you meant == (comparison). This doesn’t compile:

if condition = true {
    // The program does not compile
}

The assignment operator doesn’t return a value, and an if condition must be a boolean expression. So the compiler stops you before that typo reaches your users.

Swift conditionals: the if statement