A small technical doubt in C Programming

A Small technical doubt

Reply if anyone knows

This is a small pgm,Compile in gcc and see the result

#include<stdio.h>
#include<math.h>
int main()
{
float a=0;
printf(“\n %f \n”,a*-1);
printf(“\n %f \n”,abs(a*-1));
return 0;
}

I got the result as follows

-0.000000

Why is it so?

c language, doubt, programming

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This entry was posted by Sabin on October 6, 2010 at 10:35 PM, and is filed under Computer Science, Technical. Follow any responses to this post through RSS 2.0. You can leave a response or trackback from your own site.

Comments (6)

#1 written by TheAnand
about 1 year ago

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i give up….anyone knows the answer?
#2 written by TheAnand
about 1 year ago

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Here is your answer

http://praseedp.blogspot.com/2010/10/cc-programming-riddle.html

By Praseed sire, one of the active barcampers and someone who knows his code!
- #3 written by Sabin
  about 1 year ago
  
  Reply Quote
  
  The answer is very interesting..
  I think everyone should go through it..
#4 written by Praseed Pai
about 1 year ago

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Here is why it is so @
http://praseedp.blogspot.com/2010/10/cc-programming-riddle.html
#5 written by A C coder
about 1 year ago

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Your code is broken in lots of ways. abs() is defined in stdlib.h, not math.h. In the first printf statement, you are passing an integer to a float specifier. And in the second, you are attempting to take the absolute value of a floating point value with abs(), whose argument is clearly defined in the library as int. Having said that, gcc is just broken. Here’s what a good compiler returns when attempting to compile this junk:

$ cc t

printf(“\n %f \n”,abs(a*-1));
………………^
%CC-I-IMPLICITFUNC, In this statement, the identifier “abs” is implicitly declared as a function.
at line number 7 in file MY_DISK:[000000]T.C;2

printf(“\n %f \n”,abs(a*-1));
………………^
%CC-W-OUTFLOATINT, In this statement, this argument to printf and conversion specifier “%f” combine integer and floating-point types. Behavior can be unpredictable.at line number 7 in file MY_DISK:[000000]T.C;2

printf(“\n %f \n”,abs(a*-1));
………………….^
%CC-I-INTRINSICCALL, In this statement, an apparent invocation of intrinsic function “abs”, argument number 1 is of type “double”, which is not consistent with the expected type “int”. It will be treated as an ordinary external call at line number 7 in file MY_DISK:[000000]T.C;2

If you choose to ignore all these compilation issues, you deserve everything you get.
- #6 written by Sabin
  about 1 year ago
  
  Reply Quote
  
  Thank you friend….
  but why gcc is not giving any warning/error since I didn’t include stdlib.h .
  Also as in the first printf statement I got -0.0 while doing calculations, and this in turn led to many other complications such -0.0 is taken as negative in some situations.(only SOMETIMES, not always and I did tried to fix with and without abs() )…
  And one more thing I have to share with the readers is I made the mistake that, for float it is fabs() and not abs().