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Long long, unsigned, C & C++ issues

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Long long, unsigned, C & C++ issues

 
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  #1
Feb 24th, 2008
Hello,

I'm trying to solve an ACM problem "Light, more light". The problem is actually solved, but I can get it accepted. So browsing Internet I found a C code, which is accepted:

C++ Syntax (Toggle Plain Text) 
  1. #include<stdio.h>
  2. #include<math.h>
  3.  
  4. int main(void) {
  5. 	long long int n;
  6. 	while(scanf("%lld", &n)==1) {
  7. 		if(n==0)
  8. 			break;
  9. 		else if( (long long int)sqrt((double)n) * (long long int)sqrt((double)n) == n)
  10. 			printf("yes\n");
  11. 		else
  12. 			printf("no\n");
  13. 	}
  14. 	return 0;
  15. }

However, it doesnt' work in Eclipse's console (MinGW GCC toolchain). Why is that?

But the main problem is not that. The task states, that the number won't exceed 2^32 - 1, so in my own solution I used unsigned int:

C++ Syntax (Toggle Plain Text) 
  1. #include <stdio.h>
  2. #include <math.h>
  3.  
  4. int main() 
  5. {		
  6. 	unsigned int n;	
  7. 	while (scanf("%d", &n) == 1)
  8. 	{			
  9. 		if (n == 0) 
  10. 			break;
  11. 		else 
  12. 		{
  13. 			unsigned int root = (unsigned int)sqrt((double)n); 
  14. 			if (root*root != n) 
  15. 			{	
  16. 				printf("no\n");
  17. 			}
  18. 			else 
  19. 			{
  20. 				printf("yes\n");
  21. 			}			
  22. 		}
  23.  
  24. 	}
  25.  
  26. 	return 0;
  27. }

... which is almost the same, works fine in Eclipse's console, but doesn't get accepted on ACM neither as ANSI C, nor as C++. Can anyone tell me where is the mistake?
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Re: Long long, unsigned, C & C++ issues

 
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  #2
Feb 24th, 2008
what are the errors when you attempt to compile on ACM?
Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.
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Re: Long long, unsigned, C & C++ issues

 
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  #3
Feb 24th, 2008
Is simply says "Wrong answer".
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Re: Long long, unsigned, C & C++ issues

 
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  #4
Feb 24th, 2008
the problem with the code using unsigned it is that nowhere in the c++ standard does it say
std::numeric_limits<unsigned int>::max() >= 2^32 - 1 or for that matter,
std::numeric_limits<unsigned int>::radix == 2 or
std::numeric_limits<unsigned int>::digits >= 32 .
so the code may fail for some input values on some implementations.

the code that was accepted is neither ISO C++ nor ANSI C. neither talks about a type long long.
the C99 standard introduced the long long int type ( to be an integral type with at least 64 bits) and it is a long-supported extension by almost all compilers. (C++0x adds this type as well as unsigned long long as fundamental types). by now, long long int (abbreviated as long long) has become a de facto standard (it is de jure only in C99). which is probably why it was accepted.
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