Why does the ++Index operator start at 0 and not 1 in this for loop?

Question

When this loop runs, it prints the value of 0 first, instead of printing 1 The initializer is set to 0, however the ++Index should be 1? I am confused

var index: Int
for index = 0; index < 3; ++index {
    print("index is \(index)")
}
// index is 0
// index is 1
// index is 2
print("The loop statements were executed \(index) times")
// prints "The loop statements were executed 3 times"

Answer 1 · 2015-12-23T21:28:39Z

December 23, 2015 9:28pm

The three parameters you use in your for loop are counter, qualifier, incrementor.

It starts the loop with the counter value, which is 0
Evaluates the loop conditional, which is less than 3
Then does the loop printing the counter at 0
Completes the loop, then applies the incrementor
Loops and evaluates 1 is less than 3
Then does the loop again printing counter at 1
Completes the loop, then applies the incrementor
Loops and evaluates 2 is less than 3
Then does the loop again printing counter at 2
Completes the loop, then applies the incrementor
Loops and evaluates 3 is not less than 3
Ends the for loop

Makes sense?

Answer 2 · 2016-02-28T17:26:44Z

February 28, 2016 5:26pm

The increment portion of the for loop happens at the end of the each iteration. So translated to the while loop you would get the following

var index: Int = 0

while index < 3 {
  print("index is \(index)") // index is still 0 here
  ++index // index is now 1
}

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Juan Bermudez

Juan Bermudez

Why does the ++Index operator start at 0 and not 1 in this for loop?

2 Answers

Nathan Tallack

Nathan Tallack

Ryan Huber

Ryan Huber