【Swift 60秒】33 - Exiting multiple loops

0x00 Lesson

If you put a loop inside a loop it’s called a ​​nested​​ loop, and it’s not uncommon to want to break out of both the inner loop and the outer loop at the same time.

As an example, we could write some code to calculate the times tables from 1 through 10 like this:

for i in 1...10 {
  for j in 1...10 {
    let product = i * j
    print("\(i) * \(j) is \(product)")
  }
}

If we wanted to exit part-way through we need to do two things. First, we give the outside loop a label. like this:

outerLoop: for i in 1...10 {
  for j in 1...10 {
    let product = i * j
    print("\(i) * \(j) is \(product)")
  }
}

Second, add our condition inside the inner loop, then use ​​break outerLoop​​ to exit both loops at the same time:

outerLoop: for i in 1...10 {
  for j in 1...10 {
    let product = i * j
    print("\(i) * \(j) is \(product)")
    if product == 50 {
      print("It's a bullseye!")
      break outerLoop
    }
  }
}

With a regular ​​break​​​, only the ​​inner​​​ loop would be ​​exited​​​ - the ​​outer​​​ loop would ​​continue​​ where it left off.

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