danijar - 2 months ago 23

C++ Question

How can I iterate over a n-dimensional array in C++ given the number of dimensions and the size of each as variables?

`int n;`

int size[n];

Since the number of dimensions is not fixed, I cannot write a nested loop for each dimension. I need the code to work with each number of dimensions.

In addition, it doesn't matter weather the actual data is stored in a n-dimensional array or a flat array containing all the data in a large row. Both are acceptable.

`int data[16][42][14]; // n-dimensional array`

int data[16 * 42 * 14]; // flat array containing the same data

Answer

You could use recursion, for each dimension "guess" its index and recursively invoke on a smaller problem, something along the lines of (peudo code):

```
iterate(d,n,size,res):
if (d >= n): //stop clause
print res
return
for each i from 0 to size[d]:
res.append(i) //append the "guess" for this dimension
iterate(d+1,n,size,res)
res.removeLast //clean up environment before next iteration
```

where:

`d`

is the currently visited dimension`size`

,`n`

is the input`res`

is a vector representing the current partial result

invoke with `iterate(0,n,size,res)`

, where `res`

is initialized to an empty list.

C++ code should be something like:

```
void iterate(int d,int n,int size[], int res[]) {
if (d >= n) { //stop clause
print(res,n);
return;
}
for (int i = 0; i < size[d]; i++) {
res[d] = i;
iterate(d+1,n,size,res);
}
}
```

full code and a simple example are available on ideone