Apex Trigger error ('Unexpected token ':' ')

Question

I've written this trigger, but there's an error that I can't resolve

The Trigger:

trigger AmounTtoWords on Receipt__c (before insert, before update) {
  for (Receipt__c **:** Trigger.new) {
        if (Total_Amount_Due__c != null && Total_Amount_Due__c >= 0) {
         
            Long n = c.Amount.longValue();
            string amo = ConvertCurrencyToWords.english_number(n);
            string amo1 = amo.remove(',');
            c.Amount_in_Words__c = amo1;
        } else {
            c.Amount_in_Words__c = null;
        }
    }
}

The Error:

Answer 1

As others mentioned in the comments already, you need to give a name to your variable. Also, you need to specify on which record you want to reference that field. So fixed code would look like:

for (Receipt__c c: Trigger.new) {
    if (c.Total_Amount_Due__c != null && c.Total_Amount_Due__c >= 0) {
        // Rest of your logic here
    }
}

Also, I guess that c should be your receipt, so I called it like that to minimize the changes you would need to do to your code. But please give your variables some meaningful names.
And think about using some sort of a trigger framework, best practice is to have 1 line triggers that call your trigger framework and not having any logic inside your triggers.