multiple if statements in SWIFT 3

 @IBAction func addtoCart(_ sender: Any) {

    if  UserDataSingleton.sharedDataContainer.is_guest == "guest"  {

       //segue, user is a guest 
    }


    if sizebtn.isHidden == false {
    if Size.selectedItem == nil {
        // show alert , nothing is selected from items
        }

    } else {
    // do API call

            } 

        }

    }
    }

The code above skips api calls if the user is not a guest and has selected something from item. How can I check if :

1- user is not a guest

2- if UIButton isn't hidden and user has selected from item