Static array and Dynamic array in a function - c++

Question

I have a question as below C++ code.
this is the code(No function) that can successful execute.
#include <iostream>
using namespace std;
int main()
{
int size_3 = 3;
//arr1 is a static array
int arr1[3][3] = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} };
//arr2 is a dynamic array
int** arr2 = new int* [size_3];
for (int i = 0; i < size_3; i++) {
arr2[i] = new int[size_3];
}
int val = 9;
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
arr2[i][j] = val--;
}
}
cout << "Elements in matrix 1: " << endl;
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
cout << arr1[i][j] << " ";
}
cout << endl;
}
cout << endl;
cout << "Elements in matrix 2: " << endl;
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
cout << arr2[i][j] << " ";
}
cout << endl;
}
cout << endl;
int** prod_arr = new int* [size_3];
for (int i = 0; i < size_3; i++) {
prod_arr[i] = new int[size_3];
}
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
prod_arr[i][j] = 0;
for (int k = 0; k < size_3; k++) {
prod_arr[i][j] += arr1[i][k] * arr2[k][j];
}
}
}
cout << "Elements in the product of 2 matrices: " << endl;
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
cout << prod_arr[i][j] << " ";
}
cout << endl;
}
}
However, I am gonna to use the function for the multiplication of the 2 matrices.
how could I move it to function, since the first array is static array, the second array is dynamic array.
I have try different way to use pointer , pass-by reference in the function, but still can't work.
My invalid code as below.
#include <iostream>
using namespace std;
int** function(int farr1, int farr2, int size3) {
int** prod_arr = new int* [size3];
for (int i = 0; i < size3; i++) {
prod_arr[i] = new int[size3];
}
for (int i = 0; i < size3; i++) {
for (int j = 0; j < size3; j++) {
prod_arr[i][j] = 0;
for (int k = 0; k < size3; k++) {
prod_arr[i][j] += farr1[i][k] * farr2[k][j];
}
return prod_arr[i][j];
}
}
}
int main()
{
int size_3 = 3;
//arr1 is a static array
int arr1[3][3] = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} };
//arr2 is a dynamic array
int** arr2 = new int* [size_3];
for (int i = 0; i < size_3; i++) {
arr2[i] = new int[size_3];
}
int val = 9;
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
arr2[i][j] = val--;
}
}
cout << "Elements in matrix 1: " << endl;
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
cout << arr1[i][j] << " ";
}
cout << endl;
}
cout << endl;
cout << "Elements in matrix 2: " << endl;
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
cout << arr2[i][j] << " ";
}
cout << endl;
}
cout << endl;
int** prod_arr = function(farr1, farr2, size_q3);
cout << "Elements in the product of 2 matrices: " << endl;
for (int i = 0; i < size_3; i++) {
for (int j = 0; j < size_3; j++) {
cout << prod_arr[i][j] << " ";
}
cout << endl;
}
cout << endl;
}
I want to use the function to execute the code.
I got 2 array, one is static and another is dynamic,
How to use pointer and pass to function with this different arrays.
Thanks a lot for your help.

Answer 1

Some C++ array examples to get you started :
A 2D dynamically array can be modeled as std::vector<std::vector<int>>
#include <array> // static array
#include <vector> // dynamic array, can resize at runtime
#include <iostream>
// https://en.cppreference.com/w/cpp/container/array
// accept a modifiable static array (content can be changed
// the & means by reference, the array will not get copied
// https://isocpp.org/wiki/faq/references
void func1(std::array<int, 4>& values)
{
values[2] = 3;
}
// array cannot be modified in body of func2 only used : const
void func2(const std::array<int, 4>& values)
{
std::cout << values[2] << "\n";
}
// https://en.cppreference.com/w/cpp/container/vector
// return a dynamically allocated array of integers
// it will have a size of 5 when returned
std::vector<int> get_values()
{
return std::vector<int>{1, 2, 3, 4, 5};
}
int main()
{
auto values = get_values();
values.push_back(6); // add another value
// https://en.cppreference.com/w/cpp/language/range-for
// prefer to use those if you don't need indices
// (which is not as often as you think)
for (const int value : values)
{
std::cout << value << " ";
}
return 0;
}