I have a string that returns from a Web API:
example:
string res = "refno=11111&status=0&deldate=2023-07-16"
how to get the value of refno, status and deldate?
That's called a "query string". You can use HttpUtility.ParseQueryString
to get the pieces, if you don't want to parse the string yourself.
https://learn.microsoft.com/en-us/dotnet/api/system.web.httputility.parsequerystring?view=net-7.0