[SalesForce] Execute anonymous Unexpected Token

The following code will solve your problem:

public class ContactSearch {
    public static List<Contact> searchForContacts(String lastName, String mailingPostalCode) {
        List<Contact> retList = [SELECT Id, Name, LastName, MailingPostalCode
                                 FROM Contact
                                 WHERE LastName = :lastName AND MailingPostalCode = :mailingPostalCode];
        return retList;
    }   
}

Let's view it line-by-line:

public class ContactSearch

This is just a class definition. Public says that this class is in public scope

public static List<Contact> searchForContacts(String lastName, String mailingPostalCode)

This is method declaration. Again, public keyword makes this method public accessible(public scope).
Static means that this method is class-method(static-method) and not instance-method. Difference is that for instance-method you would omit static keyword, but you would need an instance of that class to call this method.
List<Contact> is return type of the method. It means that this method will return a List of Contact objects.
searchForContacts is method name, use it to call this method.
String lastName, String mailingPostalCode are parameters that are expected by this method.

List<Contact> retList = [SELECT Id, Name, LastName, MailingPostalCode
                                 FROM Contact
                                 WHERE LastName = :lastName AND MailingPostalCode = :mailingPostalCode];

This line assigns the result of the query to retList variable.
List<Contact> retList makes a variable with name retList of type List<Contact>.
SELECT Id, Name, LastName, MailingPostalCode FROM Contact is a simple query that will return all contacts. However, you only need the ones that match given parameters, so the next line of the query is:
WHERE LastName = :lastName AND MailingPostalCode = :mailingPostalCode
This adds a filter to the query, so that it will only return results which match LastName and MailingPostalCode with given parameters.

Note the : in the query before the parameters:

If you want to use variables in your query, they should have : in front. That tells your code that it's not the value to be searched for, but a variable from the code

return retList; will return the list of matching contacts that you just found

update: alternativly, instead of creating a retList variable, you could immediately return the query. Like this:

public class ContactSearch {
        public static List<Contact> searchForContacts(String lastName, String mailingPostalCode) {
            return [SELECT Id, Name, LastName, MailingPostalCode
                                     FROM Contact
                                     WHERE LastName = :lastName AND MailingPostalCode = :mailingPostalCode];
        }   
    }

The Developer Console is using the REST version of the Tooling API to perform the execute anonymous call. The length issue is a restriction of how the call encodes the apex into the URL.

/executeAnonymous/?anonymousBody= <url encoded body>

It is URL encoding your Apex onto the query string. Clearly there are limits to how long this can be.

I found a few viable alternatives.

1. Create a temporary Apex class with the anon Apex in a static method. Then call that static method from Anon Apex. This works, but kind of defeats the purpose of anon apex.
2. Use a tool (or direct call) that runs the Anonymous Apex via the SOAP API. The SOAP API puts the anonymous Apex in the SOAP POST request, so it doesn't care what the length is (beyond the Apex upper limits on class size).
3. You can also run Anonymous Apex code via the older Apex SOAP API.