define constants

What is the best way to define constants in a C++ header file? Currently I am using the following format.

constant.H

//Define constants


#define Grids 70
#define Hori_L 10.0
#define delta_x Hori_L/(Grids - 1)

#define P0 101325 //N/(m^2)
#define T0 300 //kg/(m^3)

#define P1 0.9395*P0
#define T1 0.9823*T0 //K
#define rho1 P1/(R*T1) //kg/(m^
#define rho0 rho1/(0.9564)

This some times gives me strange errors as i have to put (delta_x) around them when in use
ie

Q_predicted = Q - delta_t/(delta_x)*delta_X(F, 1) + delta_t*HH;

Shuo

So why not put the ()'s inside the defined value?

http://cboard.cprogramming.com/showthread.php?t=92199

OK, so I change my answer to, "So why not actually read what you've already been told?" amongst a few insults about being lazy.....

Why use #define when a const double would do just fine?

Also, if you want const unsigned int types, it's permissible to do

Code:

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enum { P0 = 101235, T0 = 300 };

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But if you're going to have floating points in the mix as well, then just use doubles for the whole ordeal. It'll be nice and clean.

Quote:

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Also, if you want const unsigned int types, it's permissible to do

---

I'm pretty sure that enum values can be ordinary ints, so don't depend on unsigned-ness. Actually, on all compilers I can think of at the moment enums are signed values.

There are lots of threads about how to define constants, for example: http://cboard.cprogramming.com/showthread.php?t=88533