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iOS Swift Basics (retired) Control Flow While and Do-While Loop

Ben Manson
Ben Manson
5,882 Points
Posted by Ben Manson
Ben Manson
5,882 Points

It looks like my output is what they're asking for! What do I do?

Help!

while_loops.swift 
let numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

var index = 0

while index < 1 {
    println(numbers)
    index++
}

3 Answers

Dan Johnson
Dan Johnson
40,533 Points
Dan Johnson
Dan Johnson
40,533 Points

The output looked correct since you ended up printing the entire list once instead of each element on its own. Here's one solution:

// There are ten elements in the array, so we want the range 0-9.
// We can have the count property get this length for us so we
// don't have to worry about updating it or making a mistake.
while index < numbers.count {
    // Grab the element at the current index.
    // Passing just numbers in will print the entire
    // array.
    println(numbers[index])
    index++
}
Ben Manson
Ben Manson
5,882 Points
Ben Manson
Ben Manson
5,882 Points

so the index is a variable containing an integer... we initially assign it the value 0, but as it runs through the loop the value increases by one each time the loop runs, until it reaches the value specified by numbers.count, whose value is determined by the number of items in the array. Then the loop terminates. Correct?

Oh yeah! Dan, also: I see that the value of index only increases by 1 each time the loop goes through because of the index++ command, which is why loop terminates after it runs 10 times (10 being the value of numbers.count).

So why does adding [index] within the parenthesis have the loop print only individual items within the array rather than the whole array?

Thanks for your help with you first response!

Dan Johnson
Dan Johnson
40,533 Points
Dan Johnson
Dan Johnson
40,533 Points

numbers refers to the array itself, the collection of elements. numbers[index] refers to a specific element contained within that collection at position index.

Ben Manson
Ben Manson
5,882 Points
Ben Manson
Ben Manson
5,882 Points

Oh! I think I get it now!

so the first time the loop runs, the value of index is 0, so it'll print the first time in the first time of the index (it's as if the square brackets said [0]), the second time the value of index will be 1, so it'll print the second item (it's as if the square said said [1]), and so on until the loop terminates. That's very cool!

Thanks, Dan!

Kris B
Kris B
11,583 Points
Kris B
Kris B
11,583 Points

Your code would print 1 and stop. This is because of the "index < 1". You're saying print out the indexes less than 1. They're asking for 1 - 10. The below code will complete the task:

let numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

var index = 1

while index <= 10 {
  println(index)
  index++
}

Remember the logical operator < just means less than, <= means less than or equal to, so its required to print 10. You also need to set the index (counter) to 1 otherwise it prints 0 - 10, not 1 - 10.