can someone help me with 3d arrays

Question

Hello I'm fairly new to programming. I took an intro to Java class and I'm taking c++.

My question is, in a 3D array:

int myArr[a][b][c];

which is the one that defines the layers? a or c?

Spiral rule: myArr is an array of a arrays of b arrays of c ints. — Qaz
– Qaz, Commented Oct 23, 2013 at 1:54
Something you may need to know, but the entire array will be stored sequentially in memory. — Kirk Backus
– Kirk Backus, Commented Oct 23, 2013 at 2:59

ThunderGr · Accepted Answer · 2013-10-23 02:56:24Z

4

The way arrays are allocated in C++, you will have a blocks, each pointing to a b block each pointing to a c block. Like this:

 a -> b -> c
           c
           c
      b -> c
           c
           c

So, I would say a is defining the layers.

answered Oct 23, 2013 at 2:56

ThunderGr

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Comments

Yu Hao · Accepted Answer · 2013-10-23 07:27:26Z

3

a would be the variable defining the number of "layers", if you mean each "layer" is a 2d grid of b x c elements.

edited Oct 23, 2013 at 7:27

Yu Hao

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answered Oct 23, 2013 at 2:04

Lloyd Crawley

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1 Comment

Fert09 Over a year ago

so in an array [2][3][4] the array is of 3x4 and has 2 layers?

yano · Accepted Answer · 2013-10-23 01:56:39Z

1

When declaring and using a multi-dimensional array, it's up to you to determine which each level of the array means.

int myArray[6][3][9]

Given this array, just remember that the first index (closest to the variable name) has indicies 0-5, the middle index has indicies 0-2, and the last index has indicies 0-8. As long as you are in bounds for each, you will be fine.

answered Oct 23, 2013 at 1:56

yano

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3 Comments

Jerry Coffin Over a year ago

There is more to it than that. When you're iterating through a large array (of more than one dimension) iterating through the elements in the same order they appear in memory can improve cache usage and therefore give much higher performance (I've seen more than 10:1) speed differences.

Fert09 Over a year ago

so I can make the 9 be my number of layers as well as the 6?

yano Over a year ago

@Fert09 There's no restriction on indicies other than memory.

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