In Objective-C Generates alpha-numeric-random string

// Generates alpha numeric random string

- (NSString *)genRandomStringLength:(int)Len {

    static NSString *letters = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

    NSMutableString *randomString = [NSMutableString stringWithCapacity: len];

    for (int i=0; i<len; i++) {

        [randomString appendFormat: @"%C", [letters characterAtIndex: arc4random() % [letters length]]];

    }

    return randomString;

}