Question

I have a constant for pi in my code:

const float PI = acos(-1);

Would it be better to declare it as a double? An answer to another question on this site said floating point operations aren’t exactly precise, and I’d like the constant to be accurate.

Answer 1

From standard:

There are three floating point types:
float, double, and long double. The
type double provides at least as much
precision as float, and the type long
double provides at least as much
precision as double.

Of the three (notice that this goes hand in hand with the 3 versions of acos) you should choose long double if what you are aiming for is precision (but you should also know that after some degree, further precision may be redundant in some cases).

So you should use this to get the most precise result from acos

long double result = acos(-1L);

(Note: There might be some platform specific types or some user defined types which provide more precision)