What's wrong with my codes?

I write this codes to solve the challenge in chapter 18. It’s failed after running. and tell me reason: “_readline”, referenced from: **
** _main in main.o

ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
and that’s the codes below:

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

int main(int argc, const char * argv[]) {
_ @autoreleasepool {_
_ _
_ NSString *ask = @“who is smart?”;_
_ NSLog(@"%@",ask);_
_ const char *answer = readline(NULL);_
_ NSString *answer2 = [NSString stringWithUTF8String:answer];_
_ _
_ NSString *display = [NSString stringWithFormat:@"%@ is smart",answer2];_
_ NSLog(@"%@",display);_
_ // insert code here…_
_ NSLog(@“Hello, World!”);_
_ }_
_ return 0;_

Please make it easier for others to view your code, by posting it properly formatted.

To do that, simply copy and paste your code and embed it between the code tags like this: [code]<Your Code>[/code]

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

int main (int argc, const char * argv[]) {
    const char * input = readline ("Enter input and hit return: ");
    NSLog (@"input: %s\n", input);
    return 0;

To get the above code built, you also need to add a library to your project, the library that contains the object code for the function readline. The library is named libreadline.tbd in Xcode 7.3.

wow, that’s a good idea, thank you very much!!