Assuming you want a field length of 2 with leading zeros you'd do this:

 import Foundation

 for number in 1...3 {
 print(String(format: "%02d", number))
 }

output:

> 01
> 02
> 03

This requires `import Foundation` so technically it is not a part of the Swift language but a capability provided by the `Foundation` framework. Note that both `import UIKit` and `import Cocoa` include `Foundation` so it isn't necessary to import it again if you've already imported `Cocoa` or `UIKit`.


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The format string can specify the format of multiple items. For instance, if you are trying to format `3` hours, `15` minutes and `7` seconds into `03:15:07` you could do it like this:

 let hours = 3
 let minutes = 15
 let seconds = 7
 print(String(format: "%02d:%02d:%02d", hours, minutes, seconds))

output:

> 03:15:07