No idea about the second part of the last challenge in Swift 3 Collections and Control Flow :/

Hi! You are very close, but some of the syntax is incorrect, and you do not also need 2 while loops. This can also be done in one single loop --

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

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

Let's take this one line at a time.

while counter < numbers.count 

this is an alternative(and more efficient) way of doing what you did, which was

while counter < 7

If this array were to change, with values possibly being appended to it, then you would get an index out of bounds error and your program would crash. Using the .count method is a much safer way rather than hard coding it

now the next line,

sum += numbers[counter]

is done because the challenge asks to retrieve each value, and add it to the sum. You were retrieving the values, but not adding it to the sum, which can be done using the compound addition operator (+=), which is just

sum + sum = numbers[counter]

The last line:

counter += 1

was correct. By incrementing the counter, you stopped the loop from continuing forever.

I hope this helped and that you understood it all. Good luck :)