2D arrays with variable sizes as arguments C++

Question

I was going to create a function Swap() that swaps the two maximum elements of the n times m matrix A and matrix B. But I'm having error: declaration of 'A' as multidimensional array must have bounds for all dimensions except the first

void Swap(int A[][], int B[][], int n, int m)
{
    int max_A = A[0][0];
    int max_B = B[0][0];
    int index_Ai, index_Aj, index_Bi, index_Bj;
    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < m; j++)
        {
            if(max_A < A[i][j])
            {
                max_A = A[i][j];
                index_Ai = i;
                index_Aj = j;
            }
        }
    }
    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < m; j++)
        {
            if(max_B < B[i][j])
            {
                max_B = B[i][j];
                index_Bi = i;
                index_Bj = j;
            }
        }
    }
    int temp;
     temp = A[index_Ai][index_Aj];
     A[index_Ai][index_Aj] = B[index_Bi][index_Bj];
     B[index_Bi][index_Bj] = temp;
}

How should I deal with this problem? Or should I pass just two matrices as arguments and then find their sizes inside the funcion? Any help is appreciated.

Answer 1

Following you request here is a posssible implementation of your code using vector of vectors, aka 2D vector, with comments:

Live demo

#include <iostream>
#include <vector>
#include <exception>

//pass vectors by reference so the changes are reflected in the passed arguments
void Swap(std::vector<std::vector<int>>& A, std::vector<std::vector<int>>& B) {

    int max_A = A.at(0).at(0); //if indexing A[0][0], exception would not be thrown
    int max_B = B.at(0).at(0);
    int index_Ai, index_Aj, index_Bi, index_Bj;

    for (size_t i = 0; i < A.size(); i++) {
        for (size_t j = 0; j < A.at(0).size(); j++) {
            if (max_A < A[i][j]) { //indexing A[i][j] safe, cycle limited to vector size
                max_A = A[i][j];
                index_Ai = i;
                index_Aj = j;
            }
        }
    }
    for (size_t i = 0; i < B.size(); i++) {
        for (size_t j = 0; j < B.at(0).size(); j++) {
            if (max_B < B[i][j]) {
                max_B = B[i][j];
                index_Bi = i;
                index_Bj = j;
            }
        }
    }
    //standard library swap function
    std::swap(A.at(index_Ai).at(index_Aj), B.at(index_Bi).at(index_Bj));
}

int main() {

    std::vector<std::vector<int>> A = {{1, 2, 300}, {4, 9, 10, 56, 5, 6}};
    std::vector<std::vector<int>> B = {{10, 45, 2, 12, 20, 80}, {40, 45, 500, 60}};
    try{
        Swap(A, B);
    } catch(std::exception& e){ //if vectors accessed out of bounds throws exception
        std::cout << "ERROR: " << e.what() << std::endl; //we catch it here
        return EXIT_FAILURE;    
    }

    for (auto &v : A) { //test print A
        for (auto i : v) {
            std::cout << i << " ";
        }
        std::cout << std::endl;
    }
    std::cout << std::endl;
    for (auto &v : B) { //test print B
        for (auto i : v)
        {
            std::cout << i << " ";
        }
        std::cout << std::endl;
    }
    return EXIT_SUCCESS;
}

Initial array:

1 2 300
4 9 10 56 5 6

10 45 2 12 20 80
40 45 500 60

After swap:

1 2 500
4 9 10 56 5 6 

10 45 2 12 20 80
40 45 300 60