cleanup, and add user warning to `particle_container/interactive.cpp` if wrong...

cleanup, and add user warning to `particle_container/interactive.cpp` if wrong number of arguments is inputted

test/particle_container/interactive.cpp

@@ -11,6 +11,21 @@
 
 int main(int argc, char * argv[]) {
 
+    // Be nice to the users:
+    if(argc < 5) {
+        if(mpi::rank == 0)
+            std::cout << "You need to specify the following 4 arguments:" << std::endl
+                      << " box_x, box_y, box_z, rank_probe" << std::endl;
+        return 0;
+    }
+
+    if(argc > 5)
+        if(mpi::rank == 0)
+            std::cout << "WARNING! You have specified more than 4 input arguments." << std::endl
+                      << "Only the first 4 where used." << std::endl;
+
+
+
     /**************************************************************************
      * INITIALIZE:                                                            *
      *      -> MPI COMMS                                                      *