int main(int argc, const char * argv[])

{

    @autoreleasepool {

        NSString *outputString = @"1234567890!@#$%^&*()";

        NSMutableString *resultString = [[NSMutableString alloc] init];

        NSLog(@"%d", (int)outputString.length);

        for(int j=0;j<outputString.length;j++)

        {

            NSLog(@"Index = %d  Char = %@",j, [outputString substringWithRange:NSMakeRange(j, 1)]);

        }

        for(int i=0;i<20;i++)

        {

            int index  = arc4random() % outputString.length;

            NSString *indexString = [outputString substringWithRange:NSMakeRange(index, 1)];

            [resultString appendFormat:@"%d %@ ", index, indexString];

        }

        if (resultString) {

            NSLog(@"%@", resultString);

        }

        return 0;

    }

}