Circumference of circle to many decimal places

[Art]

But in C, since you usually have math.h with floating point, you wouldn’t actually do that.
This was part of a challenge with strict constraints.

To do it in C, it’s:

float circ;
float radius;
const float pi = 3.1415; // or however far you want to take it

radius = 10.0
circ = (2*pi)*radius;