Why use abs() or fabs() instead of conditional negation?

Question

In C/C++, why should one use abs() or fabs() to find the absolute value of a variable without using the following code?

int absoluteVal         


        

Answer 1

...and would you make it into a macro, you can have multiple evaluations that you may not want (side efffects). Consider:

#define ABS(a) ((a)<0?-(a):(a))

and use:

f= 5.0;
f=ABS(f=fmul(f,b));

which would expand to

f=((f=fmul(f,b)<0?-(f=fmul(f,b)):(f=fmul(f,b)));

Function calls won't have this unintended side-effects.