How to format cells in excel sheet programmatically?

Just set the appropriate property on your cell (Range) objects.

Set NumberFormat to control the cell number formatting, i.e.:

newSheet.Cells[i, j].NumberFormat = "m/d/yyyy"

Set HorizontalAlignment to control the alignment, i.e.:

newSheet.Cells[i, j].HorizontalAlignment = ExcelAlignment.xlLeft; //or Excel.XlHAlign.xlHAlignLeft

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