Question

I’m trying to pass a user-defined array (defined here as matrix1) into a function (det) with the aim of calculating the determinant.
Any help would be appreciated, I’m sure there’s an easy way to do this, but my various attempts using pointers/vectors have been futile!

#include <iostream>
#include <math.h>
#include <vector>

using namespace std;

int c, d;

int matrix1(int nS)
{
    cout << "Enter the elements of first matrix: ";
    int matrix1[10][10];
    for (c = 0 ; c < nS ; c++ )
    for (d = 0 ; d < nS ; d++ )
        cin >> matrix1[c][d];

for (c = 0 ; c < nS ; c++ )
    {   
        for (d = 0 ; d < nS ; d++ )
            cout << matrix1[c][d] << "\t";
            cout << endl;
    }
}

int det(int nS, int matrix)
{
    int det;
    int iii;
    for (iii = 0; iii < nS; iii++)
    {
        double a;
        double b;
        int c;
        for (c = 0; c<nS; c++)
        {
//          cout << (iii+c)%nS << endl;
//          cout << (nS-1) - (iii+c)%nS << endl;
        int z = (iii+c)%nS;
        cout << c << ", " << z << endl;
            a *= matrix[c][z];
            b *= matrix[c][(nS-1) - (iii+c)%nS];
        }

    det+= a-b;
    }
    cout << det << endl;
}

int main()
{
    cout << "Enter the number of rows and columns of matrix: ";
    int nS;
    cin >> nS;

    matrix1(nS);

    det(nS, matrix1);

    return 0;
}

Answer 1

You have to declare the array inside your main function for other functions to access it as well. An array declared inside a function other than main has a local scope on the stack and it gets destroyed as soon the function body gets executed.

That being said, you have two entities with the same name, a matrix array and a function. This wont compiler so make their names unique. Declare your matrix array in main like this.

int matrix[10][10] ;

Now pass it to your input function matrix1 like this.

matrix1(matrix, nS) ;

And your matrix function would be like this.

int matrix1(int matrix[][10], int nS)
{
  //code runs here
}

You can pass it to the det function as well in a similar fashion. And it is better if you make the row and column numbers as const so that you can change them later in your program easily.

const int ROWS = 10 ;
const int COLS = 10 ;

You can learn more on why the column number is passed and how a 2D array gets passed to a function in a similar answer here.

2D-array as argument to function