This is an interview question:-
Write a C program which when compiled and run, prints out a message indicating whether the compiler that it is compiled with, allows /* */ comments to nest.
The solution to this problem is given below :-
Sol:- you can have an integer variable nest:
int nest = /*/*/0*/**/1; if it supports nested comments then the answer is 1 else answer is 0.
How is this working ? I don't understand the variable declaration.
If the compiler doesn't allow nesting, the first */ will terminate the opening of the multiline comment, meaning the 0 won't be commented out. Written with some spaces:
int nest = /*/*/ 0 * /**/ 1; resulting in the code
int nest = 0 * 1; // -> 0 If it allows nesting, it will be
int nest = /*/*/0*/**/ 1; resulting in
int nest = 1; 
*/ in the file that would terminate it if it supported nesting. If that were the case then /**/0*1/**/ would not register as 0*1, but rather as a comment. With or without nesting the compiler should see this as 0*1
The short answer to "how is this working" is that:
int nest = /*/*/0*/**/1; with nested comments becomes something like:
int nest = // /* (comment level 1) // /*/ (comment level 2) // 0 // */* // */ 1; and without, the extra * makes it:
int nest = // /*/ (comment level 1) // */ 0 * // /* // */ 1; or 0*1.
Or, I think that's what's happening, but this question is pretty much a disaster. I entirely agree with Blagovest Buyukliev's comment.
int nest = /*/*/0*/**/1; If nesting is NOT allowed, the first comment's range is:
vvvvv int nest = /*/*/0*/**/1; With that comment removed (gap left for readability - the C++ preprocessor substitutes a single space, not sure about C), the next comment seen is:
vvvv int nest = 0*/**/1; With that also removed:
int nest = 0* 1; Below, the |+- line shows the scope of the outer comment, and vvvvvv indicates teh scope of the inner comment.
+---------+ | | | vvvvvv | int nest = /*/*/0*/**/1; With those comments removed:
int nest = 1; If it supports nested comments, then you'll have (Stripping the comments):
int nest = 1; If it does not, then you'll have (Stripping the comments):
int nest = 0 * 1; That is a big bag of loathsome hurt. My guess is that the third / possibly cancels the second multi-line comment block, rendering the * after the zero a multiplication, hence:
/* */0 * /* */ 1 == 0 * 1 == 0 // ==> nested comments aren't supported. If the compiler understands nested comments, it will just strip the /*/*/0*/**/ part and leave you with the int nest = 1.
Otherwise, it will see int nest = 0*1 and 0 * 1 == 0.
strlen(/*/*/"*/*/"/*"/**/). This is cool exercise for sites like code golf, but highly inappropriate as an interview question.