global class CountAssets implements Database.Batchable<sObject> {

  global Database.QueryLocator start(Database.BatchableContext context) {
      return Database.getQueryLocator([Select AccountId,Name, Quantity,Status s,UsageEndDate from Asset where Status='Purchased' or Status='Expired' ]);
  }


  global void execute(Database.BatchableContext context, List<Account> scope) {
     Account[] updates = new Account[] {};
     for (Asset a:AccountId)
     {
     if(Status=='Expired')
        updates.add(new Account(Id =(Id) ar.get('a'),Number_of_inactiveAssets__c = (Decimal) ar.get('c')));
        else
        updates.add(new Account(Id =(Id) ar.get('a'),Number_of_activeAssets__c = (Decimal) ar.get('c')));
    }
    update updates;
  }

  public void finish(Database.BatchableContext context) {
  }
}

global void execute(Database.BatchableContext context, List<Asset> scope) {
     for(Asset a : scope)
         {
            if(a.status == 'Expired)
                //your logic
            else
                //your logic
         }
         update scope;

}