Looking at "pratidin" (every day), Anuj thinks it is a tatpurush compound like "rajputra" because…

Why

Anuj is correct that two words are joined, but which TYPE of compound a word belongs to depends on what job the whole compound does, not just on how many parts it has. 'राजपुत्र' names a person (a noun); 'प्रतिदिन' instead tells us HOW OFTEN something happens ('हर दिन') and behaves like an adverb in a sentence — 'वह प्रतिदिन टहलता है' (he walks every day), where 'प्रतिदिन' modifies the verb, just as an ordinary adverb would. This kind, where the first part is an अव्यय (an indeclinable word like 'प्रति', 'यथा', 'आ', 'भर') and the whole compound stays unchanging and acts adverbially, is called अव्ययीभाव समास (avyayibhav samas). Test it: 'यथाशक्ति' (according to one's ability) behaves the same way — 'यथाशक्ति दान करो' (donate according to your ability) — the whole compound modifies the action, not naming any person or thing. His teacher is right: 'प्रतिदिन' is अव्ययीभाव समास — it functions like an adverb, unlike तत्पुरुष compounds such as 'राजपुत्र' which name a person or thing.