How to convert english numbers inside a string to Persian/Arabic numbers in Objective-C?

The simple way:

NSDictionary *numbersDictionary = @{@"1" : @"۱", @"2" : @"۲", @"3" : @"۳", @"4" : @"۴", @"5" : @"۵", @"6" : @"۶", @"7" : @"۷", @"8" : @"۸", @"9" : @"۹"};
for (NSString *key in numbersDictionary) {
  str = [str stringByReplacingOccurrencesOfString:key withString:numbersDictionary[key]];
}

Other solution more flexible with locale:

NSNumberFormatter *formatter = [NSNumberFormatter new];
formatter.locale = [NSLocale localeWithLocaleIdentifier:@"ar"];
for (NSInteger i = 0; i < 10; i++) {
  NSNumber *num = @(i);
  str = [str stringByReplacingOccurrencesOfString:num.stringValue withString:[formatter stringFromNumber:num]];
}

Note: this code wrote without IDE, it can be with syntax errors.

In swift 3:

func convertEngNumToPersianNum(num: String)->String{
    let number = NSNumber(value: Int(num)!)
    let format = NumberFormatter()
    format.locale = Locale(identifier: "fa_IR")
    let faNumber = format.string(from: number)

    return faNumber!
}

Check before force unwrap to prevent crash.

Swift 3:

However other answers are correct, there is a little problem in converting String to Int.

Converting a String to Int removes left zeros which is not good (Specially in converting cell phones and national Ids). To avoid this problem I prefer replacing each English number to Persian.

static func convertToPersian(text : String)-> String {
    let numbersDictionary : Dictionary = ["0" : "۰","1" : "۱", "2" : "۲", "3" : "۳", "4" : "۴", "5" : "۵", "6" : "۶", "7" : "۷", "8" : "۸", "9" : "۹"]
    var str : String = text

    for (key,value) in numbersDictionary {
        str =  str.replacingOccurrences(of: key, with: value)
    }

    return str
}

This method can also be used to replace numbers within text and its not necessary to have a pure number to convert to Persian.