There are two ways that you can go:
translating this to C# or
rewriting the code from scratch. There are countless examples on the net so below you'll find just a couple of pointers:
1. The first one assumes you're still using COM i.e. Excel.Sheet.
Reading Excel From C#How to automate Excel by using Visual C# to fill or to obtain data in a range by using arraysI guess that
Visual Studio Tools for Office is a prerequisite.
2. The other means dropping COM and reading Excel sheet names and cell values using database technology:
Reading and Writing Excel Spreadsheets Using ADO.NET C# DbProviderFactoryIt's good that you're using "XLS" files and not "XLSX". If your operating system is 32-bit, consider yourself lucky: using ODBC is relatively easy.
Using Office 2007/2010 files and
especially a 64-bit Windows edition opens a big can of worms. MS Jet 4.0 is incompatible with Win x64, so instead of the built-in driver, installing an additional component would be required (2007/2010 Office System Driver: Data Connectivity Components, x64 version) and the connection string will be different.