Swift 3 : How to use for loop for looping arrays - ios

Question

Scenario
Let's say I've an array = ["a", "b", "c", "d"]
I have a button function that allows me to print data in this array. I used a for loop to loop through the array.
But after the last array element(which is index[3]) is printed on the fourth click, I want it to print from the start(which is index[0]) on the fifth click.
Any help is much appreciated!
Thank you

Answer 1

For that you need to simply maintain the index of the current element for array object.
var currentIndex = 0
#IBAction func buttonClick(_ sender: UIButton) {
print(array[currentIndex])
currentIndex += 1
if currentIndex == array.count {
currentIndex = 0
}
}

Answer 2

Keep a click count var (initialize with 0) and use the following when the button is tapped:
let valToPrint = yourArray[clickCount % yourArray.count]
clickCount += 1
print("Current value = \(valToPrint)")
The % (modulos) operator will cycle clickCount through the required range.

Answer 3

You can write
let letters = ["a", "b", "c", "d"]
var index = 0
func printNext() {
print(letters[index])
index = (index + 1) % letters.count
}

Answer 4

write below code on button click
#IBAction func myButton(_ sender: UIButton) {
if sender.tag > array.count{
sender.tag = 0
}
print("array[\(sender.tag)] = \(array[sender.tag])")
sender.tag += 1
}

Answer 5

For the technical joy of it: another alternative would be to define a sequence which cycles over the elements of the array.
Given an immutable array:
class Foo {
private let array: [String]
private lazy var cyclingSequenceOverArray:
UnfoldSequence<String, Int> = sequence(state: -1) {
(state: inout Int) -> String? in
guard !self.array.isEmpty else { return nil }
return self.array[(state = (state + 1) % self.array.count, state).1]
}
init(_ array: [String]) {
self.array = array
}
func printNext() {
if let next = cyclingSequenceOverArray.next() {
print(next)
}
}
}
let foo = Foo(["a", "b", "c", "d"])
foo.printNext() // a
foo.printNext() // b
foo.printNext() // c
foo.printNext() // d
foo.printNext() // a
foo.printNext() // b
In the case where you let the array be mutable (var) and it ever becomes empty: a call to the next() method (as implemented above) of the sequence will terminate the sequence. I.e., even if the array were to be re-filled, subsequent calls to next() would still yield nil. In this case, you could let the sequence be infinite (never-terminating), simply returning a default value in case the array is nil:
class Foo {
var array: [String]
private lazy var cyclingSequenceOverArray:
UnfoldSequence<String, Int> = sequence(state: -1) {
(state: inout Int) -> String in
guard !self.array.isEmpty else { return (state = -1, "Empty!").1 }
return self.array[(state = (state + 1) % self.array.count, state).1]
}
init(_ array: [String]) {
self.array = array
}
func printNext() {
if let next = cyclingSequenceOverArray.next() {
print(next)
}
}
}
Example usage:
let foo = Foo(["a", "b", "c", "d"])
foo.printNext() // a
foo.printNext() // b
foo.printNext() // c
foo.array = []
foo.printNext() // Empty!
foo.printNext() // Empty!
foo.array = ["a", "b", "c", "d"]
foo.printNext() // a
foo.printNext() // b
foo.array[2] = "C"
foo.printNext() // C
foo.array = ["1", "2", "3"]
foo.printNext() // 1