Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

iOS Swift Collections and Control Flow Control Flow With Loops Working With Loops

Saleh Bubishate
Saleh Bubishate
1,613 Points
Posted by Saleh Bubishate
Saleh Bubishate
1,613 Points

while counter <= numbers.count { sum = sum + numbers[counter] counter += 1 } why it's wrong?

while counter <= numbers.count {

sum = sum + numbers[counter]

counter += 1 } why it's wrong for this challange

loops.swift 
let numbers = [2,8,1,16,4,3,9]
var sum = 0
var counter = 0

while counter <= numbers.count {

  sum = sum + numbers[counter]

  counter += 1
}

1 Answer

andren
andren
28,558 Points
andren
andren
28,558 Points

It is wrong because you use <= (less than or equal to) as the condition of the loop. Because indexes start at 0, the last index in a list will always be 1 less than the size of the list, since the size count starts at 1. That means that when the loop runs for the last time with count being equal to numbers.count you will end up trying to access an index that does not exist.

If you change the condition to be just < (less than) like this:

let numbers = [2,8,1,16,4,3,9]
var sum = 0
var counter = 0

while counter < numbers.count {
  sum = sum + numbers[counter]
  counter += 1
}

Then your code will pass the first task.