Cannot read property 'get' of undefined. May i know if there are any trouble shooting points.

I have mentioned everything correct, but still i am facing the issue, may i know if there are any trouble shooting points.
Code:
Component:
<lightning:combobox name="Select Instance:" aura:id="selctOrg" placeholder="Select an Option" options="{! v.orgList }" value="{!v.selectedOrg }" onchange="{! c.handleChange }"/>
js controller:
var selectedSOrg = component.find("selctOrg").get("v.value");
Error is: [Cannot read property 'get' of undefined]
Below is the code that i had in my controller and helper.
controller:
({ doinit : function(component, event, helper) { helper.fetchSBHelper(component, event, helper); } })
Helper:
({ fetchSBHelper : function(component, event, helper) {
var sOrg = component.find("selctOrg"); var selectedSOrg = sOrg.get("v.value"); alert("selectedSOrg"+selectedSOrg);
} })

I want to execute process builder action only when the opporunity owner changed from A to B and using the advance option of specific changes made to  the record. i do not want to execute action for any other change of the record but it is giving me error. Any Suggestions?

///////Visualforce////////

<apex:page standardController="Student__c" extensions="Student">
<apex:pageblock title="New Account">
<apex:pageBlockSection title="Register">
<apex:form >
<b>Username:</b> <br/>
<apex:inputText required="true" id="username" value="{!Student__c.Name}" /> <br/>
<b>Password:</b> <br/>
<apex:inputSecret required="true" id="password" value="{!Student__c.Mobile__c}"/> <br/>
<b>Email:</b> <br/>
<apex:inputText required="true" id="emailid" value="{!Student__c.Email__c}" /> <br/>
<b>Phone Number:</b> <br/>
<apex:inputText required="true" id="phno" value="{!Student__c.Height__c}" /> <br/> <br/>

<apex:commandButton value="Register" action="{!register}"/> <t/> <t/>
<apex:commandButton value="Existing User" action="{!pbck}"/> <br/> <br/>
</apex:form>
</apex:pageBlockSection>

</apex:pageblock>

</apex:page>

 

 

 

/////Controller////////

 

public with sharing class Student {
private final Student std;

public String Name{ get; set; }
public Double Height__c{ get; set; }
public String Email__c{ get; set; }
public String Mobile__c { get; set; }

list<student__c> stdlist=[select id, Name, Height__c, Email__c, Mobile__c from student__c where id=:ApexPages.currentPage().getParameters().get('id')];

public Student(ApexPages.StandardController controller) {
this.std= (Student)Controller.getRecord();
}

public PageReference pbck() {

return page.mylogin;
}

public PageReference register() {
insert stdlist;
return page.mylogin;
}

}

 

 

Im facing following errors:

1: Error: Student Compile Error: Invalid identifier: Height__c at line 5 column 13

2: Error: Student Compile Error: Incompatible types since an instance of SObject is never an instance of Student at line 12 column 19

 

 

for 1st error, i tried all the premitive data types, still that error is there.

Is there a way to get a list of Account records (parent) with no child records associated (Opportunity)  via SOQL?

I am trying to avoid doinf this in Apex, like getting the AccountId values from Opportunity and then query accounts where id not in this list.

 

Is it possible to get this list through SQOL?

Here is my query (I need only the accounts that have no associated Opportunity records):

 

SELECT a.Id, a.Name, (Select id from Opportunities) from Account a order by a.Name

 

Thanks,

Rodrigo