Meme of two women fighting while a man smokes from a pipe in the background.
The women fighting are labeled "mathematicians defining pi" and "engineers just using 3 because it's within tolerance"
The man smoking is labeled "astrophysicists" and the pipe is labeled "pi = 1"
As they should, if that's the only thing you are using it for, don't introduce a whole header file, just put the following in the constants.h or equivalent that the proj for sure has:
Yes, it's literally what math.h has defined.
If I'm not completely mistaken M_PI is not part of the C standard, so depending on your stdlib or compiler or even compiler flags you will have to define it yourself even in C.