The truth table:
task / language | C | C++
-------------------------------+-----------------------+------------------------
Declare variable length arrays | Use VLAs | not possible without
| int arr[n]; | non-standard extensions
| | but use std::vector<T>
-------------------------------+---------------------+--------------------------
Declare a variable number | not possible but | not possible but use
(i.e. n number of) such arrays | use int arr[n][k]; | vector<vector<T>>