Objective C － 2 - 随机数，可变字符串，字符串，SubString

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;

    }

}