What is the time complexity of squaring and sorting an array?

public int[] sortedSquares(int[] A) { for(int i = 0; i < A.length; i++) { A[i] = A[i] * A[i]; } mergeSort(A); return A; } 

Apparently it is O(nlogn) because of mergesort, but I am confused about the for loop. Is the time complexity of the for loop O(n) or O(1). I am thinking that it is O(1) because we only square each element once, but it could potentially be O(n) since we square n elements. Which one is correct? Thanks!