Have no idea to gain the indexes of art and artist from the URL using C# [closed]

Here is the example of gaining the index of art and artist:

static string pixivURL = "https://pixiv.net/"; // Main URL of Pixiv website
static string artistIdx = pixivArtistURL.Replace(pixivURL+"users/", ""); // Artist number/index after "https://www.pixiv.net/users/"
public static string pixivArtistURL = pixivURL + "users/" + artistIdx; // Pattern of a Pixiv artist's URL
static string artIdx = pixivArtistURL.Replace(pixivArtistURL+"artworks/", ""); // Art index/number after "https://www.pixiv.net/artworks/"
public string pixivArtURL = pixivURL + "artworks/" + artIdx; // Pattern of the URL of an artwork/submission of a pixiv artist

protected static string test1 = "https://www.pixiv.net/users/artistIdx";
protected static string test2 = "https://www.pixiv.net/artworks/artIdx";

And I am now going to get the art index and artist index for following these patterns, but I really have no idea whether I coded properly and don't even know how to test to get the example of the index. ;(