Leading zeros for Int in Swift

Question

I d like to convert an Int in Swift to a String with leading zeros  For example consider this code   for myInt in 1     3       print    myInt        Currently the result of it is   1 2 3   But I want it to be   01 02 03   Is there a clean way of doing this within the Swift standard libraries

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With Swift 5  you may choose one of the three examples shown below in order to solve your problem      1  Using String s init format     initializer  Foundation provides Swift String a init format     initializer  init format     has the following declaration   init format  String    arguments  CVarArg          Returns a String object initialized by using a given format string as a template into which the remaining argument values are substituted    The following Playground code shows how to create a String formatted from Int with at least two integer digits by using init format       import Foundation  let string0   String format    02d   0     returns  00  let string1   String format    02d   1     returns  01  let string2   String format    02d   10     returns  10  let string3   String format    02d   100     returns  100       2  Using String s init format arguments   initializer  Foundation provides Swift String a init format arguments   initializer  init format arguments   has the following declaration   init format  String  arguments   CVarArg        Returns a String object initialized by using a given format string as a template into which the remaining argument values are substituted according to the user   s default locale    The following Playground code shows how to create a String formatted from Int with at least two integer digits by using init format arguments     import Foundation  let string0   String format    02d   arguments   0      returns  00  let string1   String format    02d   arguments   1      returns  01  let string2   String format    02d   arguments   10      returns  10  let string3   String format    02d   arguments   100      returns  100       3  Using NumberFormatter  Foundation provides NumberFormatter  Apple states about it      Instances of NSNumberFormatter format the textual representation of cells that contain NSNumber objects and convert textual representations of numeric values into NSNumber objects  The representation encompasses integers  floats  and doubles  floats and doubles can be formatted to a specified decimal position    The following Playground code shows how to create a NumberFormatter that returns String  from a Int with at least two integer digits   import Foundation  let formatter   NumberFormatter   formatter minimumIntegerDigits   2  let optionalString0   formatter string from  0     returns Optional  00   let optionalString1   formatter string from  1     returns Optional  01   let optionalString2   formatter string from  10     returns Optional  10   let optionalString3   formatter string from  100     returns Optional  100

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Using Swift 5   s fancy new extendible interpolation  extension DefaultStringInterpolation       mutating func appendInterpolation pad value  Int  toWidth width  Int  using paddingCharacter  Character    quot 0 quot             appendInterpolation String format   quot    paddingCharacter   width d quot   value            print  quot I ate   pad  pieCount  toWidth  3  using   quot 0 quot   pies quot         gt   I ate 003 pies

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For left padding add a string extension like this   Swift 2 0    extension String       func padLeft  totalWidth  Int  with  String  - gt  String           let toPad   totalWidth - self characters count         if toPad  lt  1   return self           return    stringByPaddingToLength toPad  withString  with  startingAtIndex  0    self           Swift 3 0    extension String       func padLeft  totalWidth  Int  with  String  - gt  String           let toPad   totalWidth - self characters count         if toPad  lt  1   return self           return    padding toLength  toPad  withPad  with  startingAt  0    self           Using this method   for myInt in 1   3       print    myInt   padLeft totalWidth  2  with   0

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The other answers are good if you are dealing only with numbers using the format string  but this is good when you may have strings that need to be padded  although admittedly a little diffent than the question asked  seems similar in spirit   Also  be careful if the string is longer than the pad       let str    a str     let padAmount   max 10  str count     String repeatElement  -   count  padAmount - str count     str   Output  -----a str

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in Xcode 8 3 2  iOS 10 3 Thats is good to now  Sample1   let dayMoveRaw   5  let dayMove   String format    02d   arguments   dayMoveRaw   print dayMove     05   Sample2   let dayMoveRaw   55  let dayMove   String format    02d   arguments   dayMoveRaw   print dayMove     55

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Swift 5  imanuo answers is already great  but if you are working with an application full of number  you can consider an extension like this  extension String        init withInt int  Int  leadingZeros  Int   2            self init format   quot  0  leadingZeros d quot   int             func leadingZeros   zeros  Int  - gt  String           if let int   Int self                return String withInt  int  leadingZeros  zeros                    print  quot Warning    self  is not an Int quot           return  quot  quot                In this way you can call wherever  String withInt  3      prints 03  String withInt  23  leadingZeros  4      prints 0023   quot 42 quot  leadingZeros 2     prints 42   quot 54 quot  leadingZeros 3     prints 054

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Swift 3 0   Left padding String extension similar to padding toLength withPad startingAt   in Foundation  extension String       func leftPadding toLength  Int  withPad  String        - gt  String            guard toLength  gt  self characters count else   return self            let padding   String repeating  withPad  count  toLength - self characters count          return padding   self           Usage   let s   String 123  s leftPadding toLength  8  withPad   0       00000123

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Assuming you want a field length of 2 with leading zeros you d do this   import Foundation  for myInt in 1     3       print String format    02d   myInt       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     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

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Swift 4  and above you can try this also  func leftPadding valueString  String  toLength  Int  withPad  String    quot   quot   - gt  String           guard toLength  gt  valueString count else   return valueString                    let padding   String repeating  withPad  count  toLength - valueString count          return padding   valueString        call the function  leftPadding valueString   quot 12 quot   toLength  5  withPad   quot 0 quot    Output   quot 00012 quot

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Details  Xcode 9 0 1  swift 4 0  Solutions  Data  import Foundation  let array    0 1 2 3 4 5 6 7 8    Solution 1  extension Int        func getString prefix  Int  - gt  String           return    prefix   self              func getString prefix  String  - gt  String           return    prefix   self            for item in array       print item getString prefix  0      for item in array       print item getString prefix   0x        Solution 2  for item in array       print String repeatElement  0   count  2        item        Solution 3  extension String        func repeate count  Int  string  String    nil  - gt  String            if count  gt  1               let repeatedString   string    self             return repeatedString   repeate count  count-1  string  repeatedString                    return self          for item in array       print  0  repeate count  3       item

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Unlike the other answers that use a formatter  you can also just add an  0  text in front of each number inside of the loop  like this    for myInt in 1   3       println  0       myInt        But formatter is often better when you have to add suppose a designated amount of 0s for each seperate number  If you only need to add one 0  though  then it s really just your pick

[string] Leading zeros for Int in Swift

#1. Using `String`'s `init(format:_:)` initializer

#2. Using `String`'s `init(format:arguments:)` initializer

#3. Using `NumberFormatter`

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