check alphanumeric characters in string in c#
<p>i have used the following code but it is returning false but it should return true </p>

<pre><code>string check,zipcode;
zipcode="10001 New York, NY";
check=isalphanumeric(zipcode)

    public static Boolean isAlphaNumeric(string strToCheck)
            {
                Regex rg = new Regex("[^a-zA-Z0-9]");

                //if has non AlpahNumeric char, return false, else return true.
                return rg.IsMatch(strToCheck) == true ? false : true;
            }
</code></pre>
