Hi @sinaqq163 welcome to the forum community! Thank you for providing a screenshot and code. That makes it easier for us to understand your problem. Generally you’ll use a let when you know the variable will not change and you’ll use a var if you know or think the value will change. For the issue with the check list item, could you share a screen shot or let us know what the debugger might say? I am not sure how to go about the bug with the information given above.