How to break multiple nested loops in Swift

In Swift, we can break for-loop using the break keyword.

By default, break will exit the loop it is executing in.

In the following example, break is in the j loop, so it would break the j loop from executing further than 2.

for i in 1...3 {
    print("i \(i)")
    for j in 1...3 {
        print("== j \(j)")
        
        if j == 2 {
            // break j loop
            break
        }
    }
}

j wouldn't reach the third iteration. It will print up to 2.

Here is the result.

i 1
== j 1
== j 2
i 2
== j 1
== j 2
i 3
== j 1
== j 2

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How to break multiple nested loops in Swift

If you want to break the outer loop from the inner one. You have to do two things.

1. You need to name your loop.
2. Specify the loop you want to break by its name.

Label loop statement

You can name or label your loop by putting any name you want followed by a colon.

Put it before a loop statement.

label name: for i in 1...3 {
  // ...
}

Specified the loop you want to break

Once you have a name for your loop statement, you can easily specify the loop you want to break using the following syntax.

break label name

Here is the same example, but this time, we put the label on both loop statements.

iLoop: for i in 1...3 {
    print("i \(i)")
    jLoop: for j in 1...3 {
        print("== j \(j)")
        
        if j == 2 {
            // 1
            break iLoop
        }
    }
}

1 We specified the loop we want to break here. In this case, iLoop, which is the outer loop.

As a result, the i loop will end at the first iteration.

i 1
== j 1
== j 2