Interview Question of the Day (IQOD) #1

I like Why06's idea of the 'error of the day' so I figured i'd post some of the questions I have asked people while interviewing them for C++ Software Developer Positions.

These questions are usually written on a whiteboard (or printed out) and thus are meant to be answered WITHOUT the help of a compiler in an interview! So just read the code, don't copy/paste/build/run and just figure out what it does by reading.

I suggest you answer in a 'white font' so that others don't immediately see your answers

IQOD #1:
Consider the following program snippet:

Code:

#define   ABC    20
#define   XYZ    10
#define   XXX    ABC-XYZ

void main()
{
       int a;
       a = XXX * 10;
       printf("%d\n",a);
}

Question: What output is generated / is the value of 'a'?

Hmmmm... ok. Seems pretty easy. My Guess: 100

And you sir would be: Incorrect

Thanks a lot for these Black Angel =D

My guess: 100
But: I'm not sure whether or not you should have put the abc-xxx in brackets hmm actually nvm

You guys want the full answer with explanation now or tomorrow so the other guys can chime in? I can just write it in white I guess?

Originally Posted by B1ackAnge1

You guys want the full answer with explanation now or tomorrow so the other guys can chime in? I can just write it in white I guess?

Write it in white please, i will check after i think i know the answer again.

Oh... I GET IT NOW xD. That was a very skillful question. Kudos.

Still kudos, but i don't get it anymore xD.

Grr. I did infact get it, but i'm stupid.

Woops double post >_<

Highlight Post to see answer & explanation below
-----------------------------------------------
The Answer is: -80

#define works like a 'Find & Replace' before the program gets compiled ,thus the program actually sees:

Code:

#define   ABC    20
#define   XYZ    10
#define   XXX    20-10

void main()
{
       int a;
      // a = XXX * 10; This is then seen as:
      a = 20 - 10 * 10;
       printf("%d\n",a);
}

Following the standard operator order the multiplication gets performed first so you end up with 20-100 = 80;

Zeco got close by mentioning the brackets. Had we wanted to output 100 instead then placing brackets in the definition of XXX would've taken care of that: #define XXX (20-10); a = (20-10) * 10; etc

This is why i fail and am stupid.

When i previously said i got it, i had the same solution as Black angel. Then a little thing in my brain said. Are you stupid, - and * have the same operator precendence(importantness thingy). Even though i do know that * goes before -. I need to like sterilize my brain. grrr.

But now i am really anticipating your next one. These are really cool. I have to wait an entire 12-24 hours T_T.

OK. Before I see the answer last Guess: 200 or there something up with the #define statements

Originally Posted by why06

OK. Before I see the answer last Guess: 200 or there something up with the #define statements

Why06, your answer is: Incorrect

Yeh. I noticed that. I have no idea how #define works, but now I do. That's actually pretty neat, but I guess since i failed I don't get the job xD.

Originally Posted by zeco

Zeco you gotta lighten up. Your harder on urself then anyone else. I would tell you to stop calling urself stupid, but I'm not sure what weird side affect that might have with your split personality and all? o_O

Originally Posted by why06

Yeh. I noticed that. I have no idea how #define works, but now I do. That's actually pretty neat, but I guess since i failed I don't get the job xD.

Zeco you gotta lighten up. Your harder on urself then anyone else. I would tell you to stop calling urself stupid, but I'm not sure what weird side affect that might have with your split personality and all? o_O

Huh 0.0 What split personality was this again? >_< I am quite forgetful xD.

BlackAnge1, how many chances do you usually give a candidate to answer correctly? And do they have Pen and paper to work with? I'm just curious =D.

Originally Posted by zeco

BlackAnge1, how many chances do you usually give a candidate to answer correctly? And do they have Pen and paper to work with? I'm just curious =D.

Usually they get to work on the whiteboard with a dry-erase marker. Depending on the problem I'd talk them through it if they get it wrong: "Are you sure?" give them a hint and see if they get it depending on how well they're doing.

Other times I may just move on and mark them as wrong if it's a simple problem.
If you're interviewing for a C++ position but don't know the difference between i++ and ++i then that says it all right there

20 -10*10 = 20 -100 = -80 <--answer

owned

why don't u guys put all these questions together so other people can try them to?

Interview Question of the Day (IQOD) #1

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