Copy of random matrix in C - arrays

Question

Just as the title says, here I ask for two inputs in order to generate a matrix based on such inputs from the user, which then will be filled with random numbers up to the number 20.The problem is I can't wrap my head around the logic needed to generate an exact copy of this matrix without generating a second matrix with randomly generated numbers(again) so I can make useof the data stored in the copy.
(Edit)
I've added an image as reference of what I'm trying to achieve.
I tried to store the random values in a one dimensional array, so I can use them later, but I'm not sure if it is the right approach. I'm relatively new to coding and still struggling with the basics, so any help will be greatly appreciated.
Here´s the code that generates the matrix and stores random int values in it.
#include <stdio.h>
#include<time.h>
int matrizAleatoria(int m, int n, int r);
int srand();
int rand();
int main()
{
int m, n;
printf("Introduce el numero de filas:\n");
scanf("%d", &m);
printf("Introduce el numero de columnas:\n");
scanf("%d", &n);
printf("\n");
srand(time(0));
int r = (rand()% 20);
matrizAleatoria(m, n, r);
printf("\n");
return 0;
}
int matrizAleatoria(int m, int n, int r)
{
int i, j, p = m * n;
int matriz1[m][n];
int serie[p];
for(i = 0; i<m; i++)
{
for(j = 0; j<n; j++)
{
matriz1[i][j] = r = (rand()% 20);
serie[i] = r;
printf("[ %-2d ] " , matriz1[i][j]);
}
printf("\n");
}
return serie[i];
}

Answer 1

You cannot return a variable-sized array from a function to outside scope. You have to implement 2-dimensional subscripts yourself and only work with pointers. Like this:
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#define SUBSCRIPT_2DIM_TO_1DIM(subscript1, subscript2, size2) \
((subscript1) * (size2) + (subscript2))
int* matrizAleatoria(int m, int n);
int main()
{
int m, n;
int* matriz1;
printf("Introduce el numero de filas:\n");
scanf("%d", &m);
printf("Introduce el numero de columnas:\n");
scanf("%d", &n);
printf("\n");
srand(time(0));
matriz1 = matrizAleatoria(m, n);
printf("\n");
// use matriz1 with SUBSCRIPT_2DIM_TO_1DIM
free(matriz1);
return 0;
}
int* matrizAleatoria(int m, int n)
{
int i, j, p = m * n;
// return matrix value, must free() in the caller
int *matriz1 = malloc(sizeof(int) * p);
for(i = 0; i<m; i++)
{
for(j = 0; j<n; j++)
{
matriz1[SUBSCRIPT_2DIM_TO_1DIM(i, j, n)] = rand()% 20;
printf("[ %-2d ] " , matriz1[SUBSCRIPT_2DIM_TO_1DIM(i, j, n)]);
}
printf("\n");
}
return(matriz1);
}