I have an issue that I am hoping others may have come across and/or can quickly and easily point out what I have done incorrectly in the below sequence of code. I am receiving the error Loop must iterate over collection: Boolean on Line 21 for (Case c: Trigger.isUpdate).

In case it is not clear, I just need to grab the AccountId from the Case when updated and input these into custom objects.

I am new to coding and any help or guidance would be greatly appreciated.

```java
trigger CaseAfterUpdate on Case (after update) {

    //Variables
    Set<Id> accountId = new Set<Id>();
    Map<Id,Case> allAccIds = new Map<Id, Case>();
    List<MyIns__c> updateIns = new List<MyIns__c>();
    List<MySup__c> updateSup = new List<MySup__c>();
    List<MyIns__c> newIns = new List<MyIns__c>();
    List<MySup__c> newSup = new List<MySup__c>();
    List<Case> caseList = new List<Case>();

    Schema.DescribeSObjectResult caseSchema = Schema.SObjectType.Case;
    Map<String,Schema.RecordTypeInfo> caseRecordTypeInfo = caseSchema.getRecordTypeInfosByName();
    Id rtCaseDA = caseRecordTypeInfo.get('My_Record_Type').getRecordTypeId();
    system.debug('rtCasefromschema'+rtCaseDA);

    //Id rtCaseDA = [SELECT Id FROM Recordtype WHERE DeveloperName = 'My_Record_Type' AND SObjectType='Case' LIMIT 1].Id ;

    //Update Trigger
    for (Case c: Trigger.isUpdate){

        if (c.RecordTypeId == rtCaseDA && c.Status == 'Approved') {
            //Sup Approved

            accountId.add(c.AccountId);

        }

        allAccIds.put(c.AccountId, c);

    }

    //Ins
    if(allAccIds.size()>0) {

        List <MyIns__c> newIns = [SELECT Id, Id__c, Approved__c FROM MyIns__c WHERE Id__c IN :allAccIds.keyset()];
        for(MyIns__c ins : newIns ) {
            //Update the ins to approved
            for(Case cs : allAccIds.values() ) {
                if(cs.AccountId == ins.Id__c && cs.N_Ins__c == TRUE) {
                    ins.Approved__c = True;
                    updateIns.add(ins);
                }

            }

        }
        if(updateIns.size()>0){
            update updateIns;
        }
    }

    //Sup
    if(allAccIds.size()>0) {

        List <MySup__c> newSup = [SELECT Id, Id__c, Approved__c FROM MySup__c WHERE Id__c IN :allAccIds.keyset()];
        for(MySup__c sup : newSup ) {
            //Update the sup to approved
            for(Case cs : allAccIds.values() ) {
                if(cs.AccountId == sup.Id__c && cs.N_Sup__c == TRUE) {
                    sup.Approved__c = True;
                    updateSup.add(sup);
                }

            }

        }
        if(updateSup.size()>0){
            update updateSup;
        }

    }

}

```