ISheet ICell

 /// <summary>
        /// Gets the first row on the sheet
        /// </summary>
        /// <value>the number of the first logical row on the sheet (0-based).</value>
        int FirstRowNum { get; }

        /// <summary>
        /// Gets the last row on the sheet
        /// </summary>
        /// <value>last row contained n this sheet (0-based)</value>
        int LastRowNum { get; }

/// <summary>
        /// Get the number of the first cell Contained in this row.
        /// </summary>
        /// <returns>
        /// short representing the first logical cell in the row,
        /// or -1 if the row does not contain any cells.
        /// </returns>
        short FirstCellNum { get; }
        
            /// <summary>
        /// Gets the index of the last cell Contained in this row <b>PLUS ONE</b>. The result also
        /// happens to be the 1-based column number of the last cell.  This value can be used as a
        /// standard upper bound when iterating over cells:
        /// <pre>
        /// short minColIx = row.GetFirstCellNum();
        /// short maxColIx = row.GetLastCellNum();
        /// for(short colIx=minColIx; colIx&lt;maxColIx; colIx++) {
        /// Cell cell = row.GetCell(colIx);
        /// if(cell == null) {
        /// continue;
        /// }
        /// //... do something with cell
        /// }
        /// </pre>
        /// </summary>
        /// <returns>
        /// short representing the last logical cell in the row <b>PLUS ONE</b>,
        /// or -1 if the row does not contain any cells.
        /// </returns>
        short LastCellNum { get; }

Excel2003

HSSFWorkbook

D:\ChuckLu\Git\GitHub\Other\npoi\main\HSSF\UserModel\HSSFCell.cs

 /// <summary>
        /// Returns a string representation of the cell
        /// This method returns a simple representation,
        /// anthing more complex should be in user code, with
        /// knowledge of the semantics of the sheet being Processed.
        /// Formula cells return the formula string,
        /// rather than the formula result.
        /// Dates are Displayed in dd-MMM-yyyy format
        /// Errors are Displayed as #ERR&lt;errIdx&gt;
        /// </summary>
        public override String ToString()
        {
            switch (CellType)
            {
                case CellType.Blank:
                    return "";
                case CellType.Boolean:
                    return BooleanCellValue ? "TRUE" : "FALSE";
                case CellType.Error:
                    return NPOI.SS.Formula.Eval.ErrorEval.GetText(((BoolErrRecord)_record).ErrorValue);
                case CellType.Formula:
                    return CellFormula;
                case CellType.Numeric:
                    string format = this.CellStyle.GetDataFormatString();
                    DataFormatter formatter = new DataFormatter();
                    return formatter.FormatCellValue(this);
                case CellType.String:
                    return StringCellValue;
                default:
                    return "Unknown Cell Type: " + CellType;
            }

        }

Excel2007

XSSFWorkbook

D:\ChuckLu\Git\GitHub\Other\npoi\ooxml\XSSF\UserModel\XSSFCell.cs

 /// <summary>
        /// Returns a string representation of the cell
        /// </summary>
        /// <returns>Formula cells return the formula string, rather than the formula result.
        /// Dates are displayed in dd-MMM-yyyy format
        /// Errors are displayed as #ERR&lt;errIdx&gt;
        /// </returns>
        public override String ToString()
        {
            switch (CellType)
            {
                case CellType.Blank:
                    return "";
                case CellType.Boolean:
                    return BooleanCellValue ? "TRUE" : "FALSE";
                case CellType.Error:
                    return ErrorEval.GetText(ErrorCellValue);
                case CellType.Formula:
                    return CellFormula;
                case CellType.Numeric:
                    if (DateUtil.IsCellDateFormatted(this))
                    {
                        FormatBase sdf = new SimpleDateFormat("dd-MMM-yyyy");
                        return sdf.Format(DateCellValue, CultureInfo.CurrentCulture);
                    }
                    return NumericCellValue.ToString();
                case CellType.String:
                    return RichStringCellValue.ToString();
                default:
                    return "Unknown Cell Type: " + CellType;
            }
        }