Greetings, Ive just started a few days ago with Apex by work as a junior developer at the moment, heres my issue:

This trigger needs to transfer Integer values from a custom Object called Encuesta__c(Survey__c) with its a custom object, to three custom fields (Num_Prom_Cobr__c,Num_Prom_Perp__c,Num_Prom_Sin__c) from Account after being fired.

Heres the trigger code called traspasoValoresListas (transferListValues):

trigger traspasoValoresListas on Encuesta__c (before insert , before update) {

Encuesta__c[] encu = Trigger.new;

Integer sin; /*These three Integers are to contain the upcoming values of APEX class called
Integer cob; ConvertirStringValores with functions that converts the values of a Seleccion list into Integers*/
Integer per;

for (Integer i=0;i<encu.size();i++)
{
     sin=ConvertirStringValores.convertirListasSiniestros(encu[i]);//Turns the value Selectionlist called Siniestros(Fires)(String) to Integer
     per=ConvertirStringValores.convertirListasPercepcion(encu[i]);//Turns the value Selectionlist called Percepcion(Perception)(String) to Integer
     cob=ConvertirStringValores.convertirListasCobranza(encu[i]);//Turns the value Selectionlist called Cobranza(Collections)(String) to Integer
    //All of these values coming from the Custom Object Encuesta__c assigned as encu;
}
//The code sadly goes downhill from here
Account a = [SELECT Num_Prom_Cobr__c,Num_Prom_Perp__c,Num_Prom_Sin__c
                   FROM Account];

a.Num_Prom_Cobr__c=cob;
a.Num_Prom_Perp__c=per;
a.Num_Prom_Sin__c=sin;

update a;
}

Any help is highly appreciated!
Felipe.