How to handle Child browser popup in selenium webdriver

//open browser

WebDriver driver=new FirefoxDriver();

//navigate to website

driver.get(https://www.hdfcbank.com/);

//windowhandle of parent browser

String a=driver.getWindowhandle();

System.out.print(a);

//click on login button

driver.findElement(By.id(“loginsubmit”)).click();

//Size of windowhandles  child browser

Set<String> b=driver.getWindowhandles();

System.out.print(b);

// windowhandles of  child browser

Iterator<String>c=driver.getWindowHandles().iterator();

While(c.next()){

String d=c.hasnext();

driver.switchTo().Window(d);

String aTiltle= driver.getTitle();

System.out.print(aTiltle);

}