Counter for re-opened cases - Salesforce - triggers

Question

I'm traying to create a trigger that count each time a case is re-opened.
What I need is that changing the Status "Cerrado" to "Asignado" add +1
I've this trigger but it doesn't working at all.
Reperturas__c a type number and in the formula I've a 0.
"Cerrado" close the case.
Any solution guys?. Thanks!
trigger caseReOpen on Case (before update) {
for(Case c:trigger.new){
if(trigger.Oldmap.get(c.Id).Status=='Cerrado'){
c.Reaperturas__c ++;
}
}
}

Answer 1

Should work, weird. How's this?
trigger caseReOpen on Case (before update) {
for(Case c: trigger.new){
Case old = trigger.oldMap.get(c.Id);
if(c.Status == 'Asignado' && old.Status == 'Cerrado'){
++c.Reaperturas__c;
}
}
}
Compiled and saved ok? Can you put field history tracking on it, maybe you have something else that resets the counter? Are the actual picklist values like that or are these just labels? You need to use API values in Apex so if they're in English and you just have labels translated - your code won't work.
What if you base the check on !c.IsClosed && old.IsClosed ? It's a computed checkbox, can't be edited directly but it's bit more portable... If in future you add more statuses counting as closing (closed completed, closed cancelled etc?). https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_objects_case.htm