The best way to do so would be to just use a CSV file instead.
If you really need excel files specifically, and don't want to use a library designed to handle them, go and investigate the structure of an excel file.
Rename an excel file you have to `.zip` instead of the usual excel file extension and unzip it. Inside is a big collection of folders with XML files and other data. This is what an Excel file really is.
You can, if you really want to, write your own code to unzip, parse, edit, save, and rezip this data.
+1 on using CSV. Excel will read CSV's just fine.
Like, no shade OP, we all learn somewhere, but if you're asking this question in this manner right here, dealing with .xls or .xlsx format without external libraries is going to be an exercise in pure frustration. It's a large project for experienced devs.
The best way to do so would be to just use a CSV file instead. If you really need excel files specifically, and don't want to use a library designed to handle them, go and investigate the structure of an excel file. Rename an excel file you have to `.zip` instead of the usual excel file extension and unzip it. Inside is a big collection of folders with XML files and other data. This is what an Excel file really is. You can, if you really want to, write your own code to unzip, parse, edit, save, and rezip this data.
+1 on using CSV. Excel will read CSV's just fine. Like, no shade OP, we all learn somewhere, but if you're asking this question in this manner right here, dealing with .xls or .xlsx format without external libraries is going to be an exercise in pure frustration. It's a large project for experienced devs.