How to capture last 4 characters from NSString

Use the substringFromIndex method,

OBJ-C:

NSString *trimmedString=[string substringFromIndex:MAX((int)[string length]-4, 0)]; //in case string is less than 4 characters long.

SWIFT:

let trimmedString: String = (s as NSString).substringFromIndex(max(s.length-4,0))