We index from zero because it requires the least translation to machine code. One idea in this note, however, is pernicious: 2 <= i < n. In the for statement -

We index from zero because it requires the least translation to machine code. One idea in this note, however, is pernicious: 2 <= i < n. In the for statement - for (int i = 0; i < n; i++) a[i] = i - i must take on a value that is not in the range of indices of the array, 0..n-1, to terminate the loop. This doesn't help reasoning about the loop. The problem is worse when pointer arithmetic is involved - e.g. for (p = start; p < end; p++) *p = 0 - as the final value of p may not even be a valid address. We would be better off with closed intervals and index types that restrict the range of values to those intervals.