Following code uses a third-party ZIP component from Rebex:
// add content of the local directory C:\Data\
// to the root directory in the ZIP archive
// (ZIP archive C:\archive.zip doesn't have to exist)
Rebex.IO.Compression.ZipArchive.Add(@"C:\archive.zip", @"C:\Data\*", "");
Or if you want to add more folders without need to open and close archive multiple times:
using Rebex.IO.Compression;
...
// open the ZIP archive from an existing file
ZipArchive zip = new ZipArchive(@"C:\archive.zip", ArchiveOpenMode.OpenOrCreate);
// add first folder
zip.Add(@"c:\first\folder\*","\first\folder");
// add second folder
zip.Add(@"c:\second\folder\*","\second\folder");
// close the archive
zip.Close(ArchiveSaveAction.Auto);
You can download the ZIP component here.
Using a free, LGPL licensed SharpZipLib is a common alternative.
Disclaimer: I work for Rebex