I've just started to learn C++.
I have to declare a method that will accept variables like this ones:
int grid1[200][200]; int grid2[20][25]; int grid3[53][40]; How do I have to declare that parameter in the method?
I have found this declaration, but I don't know if it is useful or how can I use it:
int** a = new int*[rowCount]; I will copy that parameter to a member variable that will be dynamic (I think it will be in the heap, so this is why it is dynamic).
For statically sized arrays, use std::array. For dynamically sized arrays use std::vector. Don't ever use raw C arrays unless some weird situation forces it on you.
If you need a multi dimensional array, you can of course use std::vector<std::vector<int>> or similar for std::array. This is easy and convenient since you can do myarray[row][column] (and possibly good enough). But a better performing option is usually to just declare a 1D std::vector<int> with a size of "dimension 1 * dimension 2" and then, when indexing into it, do myvector[row_number * size_of_row + column]. Treating a 1D array as a 2D one is as easy as that and it is likely to perform better since it's friendlier to your CPUs prefetcher and cache hierarchy.
As for declaring a function to accept such arrays - it's straight forward. For example:
void f(const std::array<int, 666>& myarray); void f(const std::array<std::array<int, 42>, 666>& myarray); void f(const std::vector<int>& myarray); void f(const std::vector<std::vector<int>>& myarray); Use std::vector and forget everything related to plain arrays.
void foo(vector<vector<int>>& v) { ... } // now you have a 100x50 double array vector<vector<int>> x; x.resize(100); for(auto& xx : x) { xx.resize(50); } foo(v); If you care about caching as the comment mentions, you can create a single dimensional vector and convert it to a multidimensional array, I had previous asked about that here for dynamic arrays. Or if your size is static you can simply:
vector<int> x(100); int(*yy)[3] = (int(*)[3])x.data(); // Creates a 2D array inside x yy[0][1] = 5; yy[1][2] = 4; yy[2][2] = 10; Doing internal calculations with rows and columns like x*col + row to manually convert a single dimension array to 2D is bad and error prone.
std::vector.int** a = new int*[rowCount];is a relic of the 1990s