Part 2 of the Code Challenge

while counter < numbers.count { 
/*counter is 0 the first time we enter the loop
* 0 is less than numbers.count which contains a total of 7 items
*/
  sum += numbers[counter];
  //sum was 0 but after we cross this line of code sum becomes the addition of the element at
  //the counter position each time we go through the loop.

  //This is equivalent to saying  sum = sum + numbers[counter]
  //first time we enter the loop sum = 0 + numbers[0] = 0 + 2
  //second time: sum = 2 + numbers[1] = 2 + 8 = 10... and so on
  counter++;
  //we have to increment counter, if we dont, we would have an infinite loop on position 0 which
  //means our code would keep running till eternity on the same position
}