I've reading some articles about collision detection. My question here is about ideas on the design for it.

Baically I have a C++ game that has a main loop with entities with an update method. Based on keyboard input, these characters updates their positions.

My question is not about how to detect collisions, it's about getting ideas in which is the best way to implement this. The game has a main character but also enemies that have to collide between them, so I'm not sure where to make all the iterations for checking collisions and if the right way is to check everything against everything.

Thanks in advance.