How can a variable be declared and initialized as an array in C?

Question

Say you are given an array which has all duplicate members except one, which out this non-duplicate member.

Answer 1

By initializing the instruction

Answer 2

I would like to give the answer with the help of an example:
int arr[] = {1,2,3};

Here arr is an array name initialized with values 1, 2 and 3.