For both sandhi and samasa, there are different rules. Every student of Sanskrit knows about the shloka which is a conversation between a king and a beggar.

Sanskrit has long been taught in conjunction with the elements of Indo-European historical grammar. Its potentialities as a means of induction of students into methods of descriptive grammar have ...

(The rules of sandhi that are common to a whole host of modern Indian languages – hima + aalaya = himaalaya, to give you the simplest example – all draw from Panini’s rules.) ...