: Create a Visual Studio project: Install the NuGet package: Create an Excel workbook: Set a default worksheet: Save the workbook: Set cell values. Set, read data from Excel file. Steps to read and write data from Excel using C: Create a new C project in Visual Studio: Add a COM component reference i.e. object: Import, like use ExcelDataReader for reading and the aforementioned EPPlus for writing. Here is an example. Here is an example of reading with: FileStream stream, File. Open filePath, FileMode.Open, FileAccess.Read. Reading from a binary Excel file, 97-xls. IExcelDataReader excelReader, ExcelReaderFactory. Start Microsoft Visual Studio. NET. On the File menu, click New, and then click Project. Select Windows Application from the Visual C project types. Form created by default. Add a reference to the Microsoft Excel Object Library. To do this, follow these steps: On the Project menu, click Add Reference. In the COM tab locate Microsoft, glad this helped. note, you can write any type of file you want, the question is whether application X will understand it. CSV file simply means comma separated values and this extension is usually opened by Excel by default. Typically, comma-separated strings or numbers of values will appear in columns, new rows will flow to the next row. Call C from an Excel workbook as a VBA macro - you can't. Access the Excel workbook from the C application – you can. It's called Microsoft Visual Studio Tools for Office, VSTO, I would disagree. You can call a C web service via a macro. I think the same applies to restful endpoints written in webapi.