What is an "array of arrays"? - Arduino - arduino

Question

I am following a tutorial about how to make a circuit involving a 4x4 keypad, multiple times a certain "vector array", you might say, has arisen that I do not know the meaning of.
I have searched around, but I have not found anything. Even on the Arduino reference sight.
Here is a code example from the video (https://www.youtube.com/watch?v=GyprsoB887Y&t=437s).
// "rows" and "cols" being defined as 4 before, so the line is essentially equal to char keys[4][4]
char keys[rows][cols] = {
{'1', '2', '3', 'A'},
{'4', '5', '6', 'B'},
{'7', '8', '9', 'C'},
{'*', '0', '#', '0'}
};
So, what is happening, specifically, it seems like an array of arrays. I see why it would have to be, it couldn't be one variable assigned to multiple arrays, it has to be a containing array that holds them. But I do see how it is declared as 4 by 4, but shouldn't it be 1 by 4? Also, what does keys[rows][columns] mean?
Couldn't it just be:
char keys[] = {
{'1', '2', '3', 'A'},
{'4', '5', '6', 'B'},
{'7', '8', '9', 'C'},
{'*', '0', '#', '0'}
};
Why isn't it?
Thanks for the help.

Answer 1

Couldn't it just be:
char keys[] = {
{'1', '2', '3', 'A'},
{'4', '5', '6', 'B'},
{'7', '8', '9', 'C'},
{'*', '0', '#', '0'}
};
Why isn't it?
It couldn't be because char keys[] specifies an array of type char. With the statement above, you are initializing each element to be an array of type char itself.
If you wanted to specify it as an array of type char, the correct way would be:
char keys[] = {
'1', '2', '3', 'A',
'4', '5', '6', 'B',
'7', '8', '9', 'C',
'*', '0', '#', '0'
};