Updating records with adding the user name

when ever user update the record that user name assign to the sales rep field.


Tigger updatesalesrep on account(before insert, before update){
   for(Account all : trigger.new){
     acc.ownerid = userinfo.getuserid();
     user user=[select name from user where id:= acc.ownerid ];
     acc.sales_rep__c = user.name;
  }
}