Why it is necessary to mention the column dimension where row dimension is optional?

Question

In array declaration

Answer 1

Look at my code example;

https://code.sololearn.com/c2DwRSriSSl0/?ref=app

A 2D array could be initialized with a fully bracketed definition e.g.

{ {1, 2, 3}, {4, 5, 6} }

or with a simple sequence of values e.g.

{1, 2, 3, 4, 5, 6}

(see http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2310.pdf chapter 6.7.9 paragraph 26)

If you choose the second way, the notation

arr[][] = {1, 2, 3, 4, 5, 6}

would be ambiguous. It could be understood as

{ {1, 2, 3}, {4, 5, 6} }

or

{ {1, 2}, {3, 4}, {5, 6} }

So the only value that can be omitted during multidimensional array initialization is the leftmost bracket value.