This is my 2e mini tutorial on Xpresso and TP.
Calculating and displaying the distance between two particles using Xpresso
In this Cinema 4d 11.5 tutorial (level = moderate), I will show you how to get / calculate the distance between two particles. This can be used to determine collisions between particles.
As an extra, I will also show you how to display the calculated the distance between two particles.
Look here.