Check whether some string exists in a comma separated string using C# .Net

Using JavaScript

<script type="text/javascript">
    window.onload = function () {
        var str = "1000,1001,1002,1003,1004";
        if (str.search('1003')) {
            alert('String found at ' + str.indexOf('1003') + 1);
        }
    };
</script>

Using C#

string str = "1000,1001,1002,1003,1004";
if (str.Contains("1003"))
{
    int pos = str.IndexOf("1003");
    string message = string.Format("string found at {0}", pos.ToString());
    ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('" + message + "');", true);
}

try this :

        const string str = "1000,1001,1002,1003,1004";
        const string checkMe = "1004";

        if (str.Contains(checkMe)) 
        {
          ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('found');", true);
        }