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# collections and control flow

Now that we have the while loop set up, it's time to compute the sum! Using the value of counter as an index value, retrieve each value from the array and add it to the value of sum.

For example: sum = sum + newValue. Or you could use the compound addition operator sum += newValue where newValue is the value retrieved from the array.

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

numbers.count
while counter < numbers.count
{
var newValue = numbers[newValue]

sum = sum + newValue

counter += 1
}
//counter = numbers[counter]
//sum = sum + counter
//print (numbers[counter])

//counter += 1
```

Hey Neymat!

If you do that counter = numbers [counter] part, you screw the counter variable which is our index to read from first to last members of the numbers array. Counter is meant to indicate our position in the array.

If variable sum has to add each value from the array in that position, we should just do something like this:

```sum += numbers [counter]
counter += 1
```

With the code you provide you do the exact same thing, but then counter loses its use as an index and we won't be able to read all the values in the array.

Hope It helps!