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Insert value into String after the last slash

I need to insert some string value after the last slash. I have such string value:
string url = "http://blog.loc/blog/news/sport/slug1_slug2_slug3-slug";
I need to get this value:
"http://blog.loc/blog/news/sport/hot_slug1_slug2_slug3-slug"
So, I need to insert hot_ (for example), after the last slash. Could anyone help me?

I know you asked for regex, but it's not really necessary in my opinion.
You can just use string.Insert:
string url = "http://blog.loc/blog/news/sport/slug1_slug2_slug3-slug";
url = url.Insert(url.LastIndexOf("/") + 1, "hot_");
url now holds the value: http://blog.loc/blog/news/sport/hot_slug1_slug2_slug3-slug

Regex Method :
string url = "http://blog.loc/blog/news/sport/slug1_slug2_slug3-slug";
var matches = Regex.Matches(url, "/");
var match = matches[matches.Count - 1];
string result = url.Insert(match.Index + 1, "hot_")

Remove the first and last parts of a URL string from AbsolutePath in ASP.NET

I'm not good with manipulating strings and could use a little help.
I'd have a URL (http://localhost/mySite/default.aspx) and I have the AbsolutePath as a string that I'm working with (/mySite/default.aspx):
string mySubUrl = Request.Url.AbsolutePath;
What I'm trying to do is remove the first and last parts of the AbsolutePath. In this example, removing "mySite" and "default.aspx", which would leave me with just "/".
There also may be instances where the URL is longer or shorter, e.g., http://localhost/mySite/mySubFolder/default.aspx, in which case after removing the first and last parts of the AbsolutePath I would be left with '/mySubFolder/'.
I did try working a little with Uri segments but didn't get too far:
string absolutePath = Request.Url.AbsolutePath;
Uri uri = new Uri(absolutePath);
string[] pathSegments = uri.Segments;

Quick solution:
string[] pathSegments = Request.Url.Segments.Skip(1).Take(Request.Url.Segments.Length - 2).ToArray();

The Request.Url.AbsolutePath already removes the left part of the Url for you, so it will give you something like /subSection/subFolder/default.aspx.
Then, you can remove the last part like this:
string absolutePath = Request.Url.AbsolutePath;
string[] urlSegments = absolutePath.Split('/');
urlSegments = urlSegments.Skip(1).Take(urlSegments.Length - 2);
string url = string.Join("/", urlSegments);

unable to read querystring in asp.net

This is my url which contains 4 querystrings(desc,url,img,title).
http://localhost:4385/Default?desc=Home%20Page&url=http://localhost:4385/&img=http://localhost:4385/images/ribbon-img.png&title=
I read querystrings like below,
string title = Request.QueryString["desc"];
string pageurl = Request.QueryString["url"];
string alttext = Request.QueryString["title"];
string imageurl = Request.QueryString["img"];
The output i get is:
title=Home Page&url=http://localhost:4385/&img=http://localhost:4385/images/ribbon-img.png&title="
it takes entire url to first querstring, this is not my expected output.
I expect values to all querystring variables
can anyone please help me

The URL format is incorrect i feel, because the slash / character will be sent as %2F in the query string but that was not done in your URL format.
Update:
Respose.Redirect("http://localhost:4385/Default?desc=Home%20Page&url="+Uri.EscapeDataString("http://localhost:4385/")+"&img="+Uri.EscapeDataString("http://localhost:4385/images/ribbon-img.png")+"&title=");

The problem is that you are not creating the QueryString with proper encoding. .NET framework has HttpUtility.ParseQueryString Method to simplify this problem of encoding. Try this code
//are you sure your URL doesn't have an ".aspx" extension?
var url = " http://localhost:4385/Default.aspx?";
var queryString = System.Web.HttpUtility.ParseQueryString(string.Empty);
queryString["desc"] = "Home Page";
queryString["url"] = "http://localhost:4385/";
queryString["image"] = "http://localhost:4385/images/ribbon-img.png";
queryString["title"] = "";
Response.Redirect(url + queryString.ToString());
Now the QueryString will look like this.
var urlWithQueryString = " http://localhost:4385/Default.aspx?desc=Home+Page&url=http%3a%2f%2flocalhost%3a4385%2f&image=http%3a%2f%2flocalhost%3a4385%2fimages%2fribbon-img.png&title="
Now parsing can be done using the method you tried
string title = Request.QueryString["desc"];
string pageurl = Request.QueryString["url"];
string alttext = Request.QueryString["title"];
string imageurl = Request.QueryString["image"]; //you have wrongly typed "img" here

How to delete string from another string position in c#

I have two string:
string url = HttpContext.Current.Request.Url.AbsoluteUri;
//give me :
//url = http://localhost:1302/TESTERS/Default6.aspx?tabindex=2&tabid=15
And:
string path = HttpContext.Current.Request.Url.AbsolutePath;
//give me:
//path = /TESTERS/Default6.aspx
Now I want to get the string:
http://localhost:1302
So what I am thinking of is I will find the position of path in url and remove the sub-string from this position in url.
What I tried:
string strApp = url.Remove(url.First(path));
or
string strApp = url.Remove(url.find_first_of(path));
but I can't find the write way to express this idea. How can I archive my goal?

So basically you want the URL, from the start up to the beginning of your path.
You don't need to "remove" that part, only take characters up to that precise point. First, you can get that location with a simple IndexOf as it returns the position of the first character that matches your string. After this, simply take the part of url that goes from 0 to that index with Substring.
string url = "http://localhost:1302/TESTERS/Default6.aspx?tabindex=2&tabid=15";
string path = "/TESTERS/Default6.aspx";
int indexOfPath = url.IndexOf(path);
string strApp = url.Substring(0, indexOfPath); // gives http://localhost:1302
Which you can shorten to
string strApp = url.Substring(0, url.IndexOf(path));

you can also do something like below code to get the Host of URI
Uri uri =HttpContext.Current.Request.Url.AbsoluteUri ;
string host = uri.Authority; // "example.com"

Here is another option.. this doesn't require any string manipulation:
new Uri(HttpContext.Current.Request.Url, "/").AbsoluteUri
It generates a new Uri which is the path "/" relative to the original Url

You should just use this instead:
string baseURL = HttpContext.Current.Context.Request.Url.Scheme + "://" +
HttpContext.Current.Context.Request.Url.Authority;

This should not be solved using string manipulation. HttpContext.Current.Request.Url returns an Uri object which has capabilities to return the information you request.
var requestUrl = HttpContext.Current.Request.Url;
var result = requestUrl.GetComponents(UriComponents.SchemeAndServer,
UriFormat.Unescaped);
// result = "http://localhost:1302"

C# Determing HTML Link Given Website

Merged with C# Convert Relative to Absolute Links in HTML String.
If I am at a given website, with a given full URL, how can I determine the absolute path of any href or src attribute.
So if I have:
string WebsiteImAt = "http://www.w3schools.com/media/media_mimeref.asp?q=1&s=2,2#a"
//Just some random website with a sub path and a filename
string text = DownloadHTML(WebsiteImAt);
string href = "/something/somethingelse/filename.asp";
//Should go to http://www.w3schools.com/something/somethingelse/filename.asp
string href2 = "something.asp";
//Should go to http://www.w3schools.com/media/something.asp
string href3 = "something";
//Should go to http://www.w3schools.com/media/something
I'm having trouble getting my regex to work with "/blah" and just "blah" without the slashes:
String value = Regex.Replace(text, "<(.*?)(src|href)=\"(?!http)(.*?)\"(.*?)>", "<$1$2=\"" + absoluteUrl + "$3\"$4>", RegexOptions.IgnoreCase | RegexOptions.Multiline);
return value.Replace(WebsiteImAt + "/", WebsiteImAt);
I cannot alter each href/src to resolve to the correct address. How do I fix my regex to account for the three href cases above?