Possible Duplicate:
How do I use arrays in C++?
In the following code snippet:
int a[2][3][2]={{{1,2},{9,8},{3,7}},{{2,2},{1,4},{5,4}}};
what will be the answers for a[i],a[i][j] ,where i<=1 and j<=2 I have no problem in understanding the a[i][j][k] working.Can you please explain how does the above indexing works?
I am not entirely sure what your problem is, but I will try to explain the indexing to you:
What you create in your example is a three dimensional array (or a nested array if you will).
I'm sure you understand simple arrays like the following
---x---
int a[3] = {1, 2, 3};
Now when you request a[x] the x will determine which position of the array is chosen.
A two dimensional array is merely an array of arrays
---------y--------
---x--- ---x---
int b[2][3] = {{1, 2, 3}, {4, 5, 6}};
When you request b[y][x] the y will determine which of the two one dimensional arrays is chosen and then the x tells you which position of that array.
A three dimensional array is only taking this one level higher: an array of arrays of arrays
----------------------z--------------------
---------y--------- ---------y---------
---x--- ---x--- ---x--- ---x----
int c[2][2][3] = {{{1, 2, 3}, {4, 5, 6}}, {{1, 2, 3}, {4, 5, 6}} };
Now a request to c[z][y][x] goes to the z-th 2d-array, then to the y-th 1d-array of that 2d-array and then to the x-th position in this array.
The requests to c[z] or c[z][y] will only result in addresses of arrays and not yield any actual int values.
a[i] and a[i][j] are addresses, it has nothing to do with the values specified in int a[2][3][2]={{{1,2},{9,8},{3,7}},{{2,2},{1,4},{5,4}}};. That means a[1]-a[0] is the number of bytes between the second array pointed by a and the first one.
a[0] = {{1,2},{9,8},{3,7}}
a[1] = {{2,2},{1,4},{5,4}}
a[0][0] = {1,2}, a[0][1] = {9,8}, a[0][2] = {3,7}
a[0][0][0] = 1, a[0][0][1] = 2, a[0][1][0] = 9, a[0][1][1] = 8, a[0][2][0] = 3, a[0][2][1] = 7
a[1][0] = {2,2}, a[1][1] = {1,4}, a[1][2] = {5,4}
a[1][0][0] = 2, a[1][0][1] = 2, a[1][1][0] = 1, a[1][1][1] = 4, a[1][2][0] = 5, a[1][2][0] = 4
The thing you have to remember here is that the there are 2 different objects you are working with.
a[i][j][k]
and
a[i][j], a[i] and a
The first is an int, the other 3 are pointers
The associated memory's look like this:
a : | a[0] | a[1]|
\/ \______________________
a[] : | a[0][0] | a[0][1] | a[0][2] | a[1][0] | a[1][1] | a[1][2] |
\/ \______________
a[][] : | a[0][0][0] | a[0][0][1] | a[0][1][0] | a[0][1][1] | ...
And so on...
Now in the example you make you do arithmic operations with pointers eg. a[1] - a[0] = 3. If you look at the memory associated wit that you can see there are 3 memory locations between the 2 pointers, thus the result is 3.
