Weird behaviour of abs in C/C++

general
, ,
1

Hi @all,

At midnight 4 am,

I was solving the question CM01 got frustrated finding the mistake in this simplest solution in C language and C++ language which went on going WA’s, later on thought to move to C++ and got AC with abs of algorithm in stl

AC solution using abs from STL C++ using abs from algorithm

Finally on single stepping realize that the abs was giving weird answers in C & C++ of stdlib.h header file so did not understood the weird behavior? Does anyone know why abs does not give correct answers in C/C++ of stdib.h while it works properly in C++ from stl.

Final AC solution in C without using abs → C Solution

P.S. Do check the input/output to understand why abs gives different answers in C than C++.

Sample Case:

Input:

1

100000000 100000000

Output:

10000000000000000

Thanks in advance!

2

The cstdlib header file abs doesn’t have a defined return type for floating point values. That is if you write abs(7.42) with cstdlib it’ll return integer 7. However with cmath header file it returns 7.42.
http://www.cplusplus.com/reference/cstdlib/abs/
http://www.cplusplus.com/reference/cmath/abs/
This is for your reference. You can clearly see here that the cstdlib abs doesn’t have a double return type. Try out for yourself. To see the difference.

4 Likes
3

Hi thank you for your link i understood my mistake, for stlib.h header file to use abs for long long integers we have llabs and not abs

Correct solutions link with abs from stdlib.h → CodeChef: Practical coding for everyone

1 Like