added comments

Author: hannorein

examples/custom_integrator/problem.c

@@ -46,16 +46,19 @@ int main(int argc, char* argv[]) {
     struct reb_simulation* r_copy= reb_simulation_copy(r);
     r_copy->integrator = REB_INTEGRATOR_LEAPFROG;
 
+    // Choose CUSTOM integrator and setup function pointers.
+    r->integrator = REB_INTEGRATOR_CUSTOM;
     struct reb_integrator custom = {
         .step = leapfrog_step,
         .synchronize = NULL,    // Not needed. step() always returns particles in synchronized state.
         .reset = NULL,          // No data stored, thus no reset required.
         .data = NULL,           // No data stored.
         .data_size = 0          // No data stored.
     };
-
-    r->integrator = REB_INTEGRATOR_CUSTOM;
     r->ri_custom = custom;
+    
+    // This would do the same as above in a more compact form (the pointers/variables default to NULL/0):
+    // r->ri_custom.step = leapfrog_step;
 
     // Integrate both simulations
     reb_simulation_integrate(r,10.);
@@ -71,6 +74,8 @@ int main(int argc, char* argv[]) {
         assert(p1.z==p2.z);
     }
 
+    printf("Simulations complete. Tests passed.\n");
+
     // Cleanup 
     reb_simulation_free(r);
     reb_simulation_free(r_copy);