Challenge:using readline()

Has anyone solve the challenge: using readline(), I do not understand the question can i cannot solve it. Any sample answer as reference?

Here’s what I got. It’s pretty straightforward when you use the chapter 8 code.

#import <Foundation/Foundation.h>
#import <readline/readline.h>

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

@autoreleasepool {
    
    printf("Where should I start counting?");
    const char *num = readline(NULL);
    NSString *newnum = [NSString stringWithUTF8String:num];
    for (int i = atoi(num); i >= 0; i -= 3) {
       NSLog(@"%@",newnum);
        if (i % 5 == 0) {
            printf("Found one!\n");
        }
    }
    
}

return 0;

}