If this string is for presentation to the end user, you should use NSNumberFormatter
. This will add thousands separators, and will honor the localization settings for the user:
NSInteger n = 10000;
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
formatter.numberStyle = NSNumberFormatterDecimalStyle;
NSString *string = [formatter stringFromNumber:@(n)];
In the US, for example, that would create a string 10,000
, but in Germany, that would be 10.000
.