Apex - do while循环

//Code for do while loop
List<apex_invoice__c> InvoiceList = [SELECT Id, APEX_Description__c, APEX_Status__c FROM APEX_Invoice__c LIMIT 20];//it will fetch only 20 records   
Integer i =0;
do {
  InvoiceList[i].APEX_Description__c = 'This is the '+i+' Invoice';
  System.debug('****Updated Description'+InvoiceList[i].APEX_Description__c);//This will print the updated description in debug log
  i++;//Increment the counter
}while (i< 1); 
//iterate till 1st record only