trigger conchangecity on Contact (after update) {
if(trigger.isafter){
if(trigger.isupdate){
set<id>conids=new set<id>();
list<account> acclst=new list<account>();
for(contact con:trigger.new){
if(con.mailingcity!=trigger.oldmap.get(con.accountid).mailingcity && con.mailingcity!=null)
conids.add(con.accountid);
}
contact con=new contact();
for(account acc:[select id,billingcity from account where id in:conids]){
acc.billingcity=trigger.newmap.get(con.accountid).mailingcity;
acclst.add(acc);
}
update acclst;
}
}

}

trigger conchangecity on Contact (after update) {
if(trigger.isafter){
if(trigger.isupdate){
set<id>conids=new set<id>();
list<account> acclst=new list<account>();
for(contact con:trigger.new){
if(con.mailingcity!=trigger.oldmap.get(con.accountid).mailingcity && con.mailingcity!=null)
conids.add(con.accountid);
}
contact con=new contact();
for(account acc:[select id,billingcity from account where id in:conids]){
acc.billingcity=trigger.newmap.get(con.accountid).mailingcity;
acclst.add(acc);
}
update acclst;
}
}

}