How to return matrix (2D array) from function? (C)

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You defined board as a local variable – its memory is dealoccated as the function goes out of scope.

You can declare the board global, or you can create it dynamically like so:

int **allocate_board(int Rows, int Cols)
{    
    // allocate Rows rows, each row is a pointer to int
    int **board = (int **)malloc(Rows * sizeof(int *)); 
    int row;

    // for each row allocate Cols ints
    for (row = 0; row < Rows; row++) {
        board[row] = (int *)malloc(Cols * sizeof(int));
    }

    return board;
}

You will need to dynamically free the board:

// you must supply the number of rows
void free_board(int **board, int Rows) 
{
    int row;

    // first free each row
    for (row = 0; row < Rows; row++) {
         free(board[row]);
    }

    // Eventually free the memory of the pointers to the rows
    free(board);
 }

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