Re^2: why the array index has to start at 0??

[ikegami]

It was something to do with boudary checks

If you want to check if a value X is in [0,N) — something that must be done very often — X % N == N will do. If N is a power of two, simpler X >> log(N) would do.

If on the other hand you were using 1-based indexes, you'd have to check if X is in [1,N], and that would require (X-1) % N == (X-1).

Many more operations are simply more natural with 0-based indexes. See Re^3: why the array index has to start at 0?? for some real-life examples.