Why is this array's row index empty?

Question

Given this array:

int arr[][2]={{3,2},{4,5},{9,7}},

What is the value of the following?

arr[2][1];

__________________________________________________________________________
So it means there are however many rows (that's why it's empty []), and two columns!

3 2
4 5
9 7

(I see the row index is left empty in general, since the computer can figure out how many rows there are. It can't tell how many columns there are, so we have to tell it.)

Answer 1

Error.
You need to separate each array with a comma like this:
{{3,2} , {x,y}...;
^^

Then the output should be 7.

{3,2}
Is the array at the 0th index.
Or: [0][]

{4,5}
Is the array at the first index
Or: [1][]

{9,7}
Is the array at the second index
Or: [2][]

So what is [2][1]
Well
[2][]: { 9, 7 }
index: 0, 1
1 is the indexOf 7. So 7 is the answer.

Answer 2

the compiler divide the values by the last indexs, the first index is the result of that.

int Array[][5] = {1,2,3,4,5, 6,7,8,9,10};
//Rows size is 2 (10/5=2)
int Array[][2][3] = {1,2,3, 4,5,6, 7,8,9 ,10,11,12};
//First index size is 2 (12/(2*3)=12/6=2)

Answer 3

well, i'm not sure if the compiler does it, but something do it

Answer 4

Oops, I edited it... Thanks!