How do you remove an item from array arduino?
There is no such concept in C. Arrays are a fixed size and that size can never be changed. You can't &quot;delete&quot; an entry. You can replace one with something else, and you can introduce the concept of a variable that says how many entries the array has, but you can't delete one.
So you could:

Keep a count of how many entries are in the array
Shuffle down all the entries one space so the unused one is at the end
Decrement the count of entries

So in your example {3, 5, 3, 6} becomes {3, 5, 6, 6} and your &quot;count&quot; holds 3 to say the first three entries are valid and to ignore the last.
Alternatively you can introduce the concept of &quot;end of array&quot;. C strings do this with the NULL character (0). Anything before that character is valid, and anything from that character onwards is ignored.  So say you nominated the value -1 to be &quot;end of array&quot; you could have, after again shuffling down the values: {3, 5, 6, -1}.
You could also have -1 (or whatever you chose) indicating an &quot;invalid&quot; entry, so your array would be {3, 5, -1, 6} and you would ignore the -1 entry in your code.