so const is used to show and make sure that a function doesnot change the data by mistake
if char is initialized then no need to mention its size but you gotta make sure that if the string is changed then it remain in the bounds or else bad things will happen so its a good measure to add const char txt = "idk somethin" to make it immutable
again sizeof says the bites of data in that datatype aka in includes the null byte and the strlen says the length of string until null byte +1 i.e. if word[20] = "hello"; then sizeof(word) is 6 and strlen is 5 where 5tn index is null byte '\0'