System.IO.Path.GetFullPath(string path)

string fileName = "myfile.ext";
string path1 = @"mydir";
string path2 = @"/mydir";
string fullPath;

fullPath = Path.GetFullPath(path1);
fullPath = Path.GetFullPath(fileName);
fullPath = Path.GetFullPath(path2);

System.IO.Path.GetFileNameWithoutExtension(string path)
string fileName = @"C:/mydir/myfile.ext";
string path = @"C:/mydir/";
string result;
result = Path.GetFileNameWithoutExtension(fileName);
result = Path.GetFileName(path);

System.IO.Path.GetDirectoryName(string path)

string fileName = @"C:/mydir/myfile.ext";
string path = @"C:/mydir/";
string rootPath = @"C:/";
string directoryName;
   
directoryName = Path.GetDirectoryName(fileName);
directoryName = Path.GetDirectoryName(path);
directoryName = Path.GetDirectoryName(rootPath);

System.IO.Path.Combine(String path1, String path2)