There might be exceptions but most of the time, proper nouns, borrowed words and one-syllable words (generally) do not change. For example: Ahmet'in, Alp'in. Hukuk-un, saat-in, sürat-e. ip-e, suç-un and so on.

It is basically same things what @saliha did but i hope it helps. the words which ending with ç, k, p, t , when get suffix a wowel or starting with wowel, latters change to c, g/ğ, b and d' respectively . ağaç-ı > ağacı kap-ın > kabın kitap-ı > kitabı yurt-u > yurdu umut-a > umuda bayrak-ı > bayrağı yaprak-ın > yaprağın sağlık-ı > sağlığı exceptions K always change to ğ . only 1 excepion . if the word ending with 2 sessiz harf (consonant) k turn to g. ahenk > ahengi kepenk > kepengin mono syllable word generally does not change . top > topa koç > koçum dut > dutu some words which came from another languages bisiklet > bisikleti hukuk > hukuku kart > karta ahret > ahreti Special names Tokat'ı Zonguldak'ı Birleşik Krallık'a but their pronunciations are changed. like Zonguldağı some pure turkish words bulutu, saçım i hope it helps. source: wiki

It depends on last letter of the word. If the last letter is f ,s, t, ı, k, ç, ı, ş, a, h, a, or p and if suffix starts with b, c, d or g , these latters change to d,g, b, c respectively , as you say . dolap+da - dolapta, aç+dı -açtı, kitap+cı - kitapçı, bit+gin - bitkin, 15+de -15'te, Türk+ce - Türkçe there is only one exception but it rarely used. Muratgil, köpekgiller***** they suppost to be Muratkil and köpekkiller but they dont. source: wiki