[w0000t]

What!? Size of the array is always known to the programmer in C. In fact, if the programmer wants to get rid of that information, he/she must deliberately do so. Once one does that, the array becomes useless.

You also haven't explained how would that size information, which we already have, magically solve the problem.

[cm2187]

A large part of overflows come from querying an array beyond its size. If the size of the array was already contained in the array (think of C# arrays which always have a Length property), developers could build more robust code that wouldn't rely on the size of the array being inferred from some other parts of the code.