Explain a bit more. How is the program outputting the data now? Is it a console applitcation or a GUI application.
If the output is currently displayed in the console, the easiest method is to redirect the output to a text file.
If it is a GUI application, you will have to "read some file handling" in C tutorials.
Rather than outputting directly to an excel worksheet, it is easiest to output the data into a Comma Seperated Value formatted file ( CSV File ), and read the data using MS Excel or Open Office Excel into a worksheet.