Ranking from fast to slow .. interview question

[GoDaddy]

I just had a technical interview ...

I had to rank from fastest to slowest ...

1)

for( int i =0;i<16;i++)
   array1[i] = array2[i];

2)

for(int i=0;i<16;i++)
    (int)array1[i] = (int)array2[i];

3)

memmove(dest,src,16);

4)

for(int i=0;i<16;i++)
  for(int j=0;j<16;j++)
      array1[i]=array2[j];

My answer : 3,1,2,4

Was it right ?

[Paul McKenzie]

The correct answer is

5) None of the above.

It depends on the compiler's optimizer. That was a trick question.

Regards,

Paul McKenzie

[GoDaddy]

:O crap

[VladimirF]

Well, this doesn't sound like an interview question. Unless you are interviewed by someone from this thread ...
BTW, you got #4 right - it does 16 times more work than #1..3. Of course, it's just writing different values over and over to the same location. Can't imagine why the speed would be an issue there.

[GoDaddy]

its a preselection test. Got tons of technical questions i had to answer on paper

[KevinHall]

Another (and probably more important question) is "What is correct"?

The call to memmove() would only be correct if both arrays had elements one byte in size.

- Kevin

BTW, (2) might effectively be the same statement as (1) if the arrays were arrays of integers.

[cilu]

It depends on the compiler's optimizer. That was a trick question.

I have this feeling that the person that asked the question did not think at that.

[Graham]

I think I'd deliberately fail that interview. A company that asks questions like that probably isn't worth working for.

[RoboTact]

I have this feeling that the person that asked the question did not think at that.

I once participated in 'competition' put by sponsor (hardware trade company) during lunch break on programming contest... They wrote some mix of C++ and Java code (mostly resembling C++) and asked tricky question about behaviour of objects with multiple inheritance and type casting. I wrote 'compile error' as answer and they ranked it as (the only) correct answer. Only two people there knew that sponsor good enough to answer in such manner.

[GoDaddy]

I think I'd deliberately fail that interview. A company that asks questions like that probably isn't worth working for.

What do you mean ?

[RoboTact]

What do you mean ?

If they asked that question with intention to actually get some 'right' order, that question is just incompetence made manifest, which doesn't speek good for the firm.

[googler]

In 2), the left hand side is not even an lvalue so it produces a compilation error.

[exterminator]

In 2), the left hand side is not even an lvalue so it produces a compilation error.

You stole that from me... I was going to reply with that until I saw your mention of it. Best regards.

[Hobson]

In 2), the left hand side is not even an lvalue so it produces a compilation error.

I think that point in 2) is that operating on ints is faster than on non-int numbers due to fact that int size should be natural data size for given architecture. Anyway, this question is not good one, I think...

Regards

[Vedam Shashank]

I think that point in 2) is that operating on ints is faster than on non-int numbers due to fact that int size should be natural data size for given architecture

int size need not be the natural data size for given architecture