Loops

Loops are used to repeatedly perform a statement(s) or block of code. In Swift, there is the for-in loop and while loop.

for-in Loop

The for-in loop is used to iterate over collections, including strings and ranges.

for char in "hehe" {
  print(char)
}

The output would be:

h
e
h
e

continue Keyword

The continue keyword will force the loop to move on to the next iteration.

for num in 0...5 {
  if num % 2 == 0 {
    continue
  }
  print(num)
}

The output would be:

1
3
5

break Keyword

To terminate a loop before its completion, use the break keyword.

for char in "supercalifragilisticexpialidocious" {
  if char == "c" {
    break
  }
  print(char)
}

The output would be:

s
u
p
e
r

Ranges

Ranges created by the ... operator will include the numbers from the lower bound to (and including) the upper bound.

let zeroToThree = 0...3

// zeroToThree: 0, 1, 2, 3

Using Underscore

An underscore _ is used instead of a placeholder variable if the variable is not referenced in the for-in loop body.

for _ in 1...3 {
  print("Olé")
}

The output would be:

Olé
Olé
Olé

stride() Function

Calling stride() with the 3 necessary arguments creates a collection of numbers; the arguments decide the starting number to the (excluded) ending number, and how to increment/decrement from the start to the end.

for oddNum in stride(from: 1, to: 5, by: 2) {
  print(oddNum)
}

The output would be:

1
3

while Loop

A while loop accepts a condition and continually executes its body’s code for as long as the provided condition is true.

If the condition is never false then the loop continues to run and the program is stuck in an infinite loop.

var counter = 1
var stopNum = Int.random(in: 1...10)

while counter < stopNum {
  print(counter)
  counter += 1
}

// The loop prints until the stop condition is met