Dynamic array size to calculate the determinant of a matrix

Question

Basically, I have written a program to calculate the determinant of a matrix.

However, this feels like quite static yet (i.e. the dimension is passed as an argument). Is there any way to make it more dynamic (without vectors) with something like pointers?

#include <bits/stdc++.h> 
using namespace std; 

#define N 4 

void getCofactor(int mat[N][N], int temp[N][N], int p, int q, int n) 
{ 
    int i = 0, j = 0; 

    for (int row = 0; row < n; row++) 
    { 
        for (int col = 0; col < n; col++) 
        { 
            if (row != p && col != q) 
            { 
                temp[i][j++] = mat[row][col]; 
  
                if (j == n - 1) 
                { 
                    j = 0; 
                    i++; 
                } 
            } 
        } 
    } 
} 
  
int determinantOfMatrix(int mat[N][N], int n) 
{ 
    int D = 0;
  
    if (n == 1) 
        return mat[0][0]; 
  
    int temp[N][N];  
    int sign = 1; 
  
    for (int f = 0; f < n; f++) 
    { 
        getCofactor(mat, temp, 0, f, n); 
        D += sign * mat[0][f] * determinantOfMatrix(temp, n - 1); 
  
        sign = -sign; 
    } 
  
    return D; 
}

Short answer - no. You can't get an array's size from a raw pointer to the array, so you have to either pass in the size as a parameter, or use a container like `std::array` or `std::vector` that carries its own size. — Remy Lebeau, Sep 09 '20 at 19:35
[`#include `](https://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h) Don't do that please! — πάντα ῥεῖ, Sep 09 '20 at 19:41
array, dynamic size, with something like pointers, that is `std::vector`. Why don't you want to use it? — 463035818_is_not_an_ai, Sep 09 '20 at 20:02
@idclev463035818 I'm learning C++ now, so I don't know all the properties of `std::vector` yet — VIVID, Sep 10 '20 at 03:36
c-arrays are super complicated, vectors are simple. Getting accustomed to c-arrays has some value, but being new to C++ is no reason to prefer them over vectors — 463035818_is_not_an_ai, Sep 10 '20 at 08:18
@idclev463035818 thank you for the response. I will start learning vectors ASAP :) — VIVID, Sep 10 '20 at 08:42

eerorika · Answer 1 · 2020-09-09T19:40:57.633

There is no way to pass a pointer to an array of dynamic size. And the inner dimensions of an array cannot be dynamic anyway.

What you can do instead is use a one dimensional dynamic array, pass pointer to element of that array as usual, and store the rows one after the other, and calculate the index based on the row size passed as an array. This results in the same layout as an array of arrays would have, but the "virtual" dimensions can be dynamic.

Dynamic array size to calculate the determinant of a matrix

1 Answers1