salesforce - Apex Triggers - Trailhead -

the code doesn't give errors, anytime run trailhead gives me message:

"challenge not yet complete... here's what's wrong: executing trigger did not work expected. "

here instructions:

for challenge, need create trigger that, before insert or update, checks checkbox. if checkbox field true, sets shipping postal code (whose api name shippingpostalcode) same billing postal code (billingpostalcode).

• the apex trigger must called accountaddresstrigger.
• the account object need new custom checkbox should have field label 'match billing address' , field name of match_billing_address. resulting api name should match_billing_address__c.
• with accountaddresstrigger active, if account has billing postal code , match_billing_address__c true, record should have shipping postal code set match on insert or update.

my code:

trigger accountaddresstrigger on account (before insert,before update) {      for(account : [select id account  match_billing_address__c = true , billingpostalcode != null])     {         a.shippingpostalcode = a.billingpostalcode;         update a;             }//end      } 

your trigger way.

trigger accountaddresstrigger on account (before insert,before update) {      //iterate accounts updated or inserted.     for(account acc :trigger.new){         //if match true set values.         if(acc.match_billing_address__c){             acc.shippingpostalcode = acc.billingpostalcode;         }     } }