[c#] How to loop through all the files in a directory in c # .net?

string[] files = 
    Directory.GetFiles(txtPath.Text, "*ProfileHandler.cs", SearchOption.AllDirectories);

That last parameter effects exactly what you're referring to. Set it to AllDirectories for every file including in subfolders, and set it to TopDirectoryOnly if you only want to search in the directory given and not subfolders.

Refer to MDSN for details: https://msdn.microsoft.com/en-us/library/ms143316(v=vs.110).aspx