how to split two strings

//Use substring expects arg starting length
string str = ("\"20v2015-04-13\"")
//for your ans try this
string strDate = str.Substring(5, 10); 

//OR
//see below link

http://csharp.net-informations.com/string/files/print/csharp-string-substring_print.htm[^]

Retrieves a substring from this instance. The substring starts at a specified character position and has a specified length. 

In complement to solution 1, which gives you an appropriate regular expression for your requirement, here is the way to use a regular expression in C#:

using System.Text.RegularExpressions;

string original = "20v2015-04-13";
Regex r = new Regex(@"(?<value>\d+)[a-zA-Z](?<date>\d{4}-\d\d-\d\d)", RegexOptions.Compiled | RegexOptions.CultureInvariant);
Match m = r.Match(original);
string value = String.Empty;
string date = String.Empty;
if (m.Success) {
   value = m.Groups["value"].Value;
   date = m.Groups["date"].Value;
}

More on regular expressions in .NET here:
System.Text.RegularExpressions Namespace[^]

<b> first Approach:</b>

 string mainstring = "20v2015-04-13";
 string[] separatevalue = mainstring .Split('v');
 string first =separatevalue[0];
 string second=separatevalue[1];


<b>second Approach:</b>

 string mainstring = "20v2015-04-13";
 string first = mainstring .Substring(0, 2);
 string second = mainstring .Substring(3, 10);

use this :

string mainstring = "20v2015-04-13";
string[] ALL = Regex.Split(mainstring , "v");
string first =ALL[0];
string second=ALL[1];

Try this:

using System;
using System.Text.RegularExpressions;

public class Program
{
    public static void Main()
    {
        string str = ("\"20v2015-04-13\"");
        Match match = Regex.Match(str, @"\d{4}-\d{2}-\d{2}|\d{2}");
        while (match.Success)
        {
            Console.WriteLine(match.Value);
            match = match.NextMatch();
        }
    }
}