A shock absorber on an automobile does one thing and one thing only, keeps the car from bouncing.
Struts are considerably different. Struts are a structural part of the suspension system where a shock is not. A strut is also a crucial part of the vehicle's steering system and greatly affects alignment angles. Camber and caster angles are usually adjusted right on the strut itself. A strut is a pivot point for the vehicles steering system and contains a coil spring. Because of this, an alignment is always needed when replacing a strut. This is also the reason that struts are typically more expensive than shocks.