Swift 3 if variable is equal to a number else error code

An if statement to determine if a user entered variable that can be used and if not output an error message

When the user enters characters through enterMoneyAmount if it's a number complete the code, if not a number print error message to moneyResults

How can I set a button to reset the number from enterMoneyAmount back to zero

var fee: Double = Double(1.20)
var tax: Double = Double(1.07)
var deposit: Double = Double(100)

@IBOutlet weak var moneyResults: UILabel!

@IBOutlet weak var enterMoneyAmount: UITextField!

@IBAction func buttonPressed(_ sender: AnyObject) {

    **if enteredMoneyAmount == Int("") {**

    let enteredAmountString = enterMoneyAmount?.text ?? ""
    let enteredAmount: Double = Double(enteredAmountString) ?? 0
    let mDeposit = enteredAmount - deposit
    let mDepositAndFee = mDeposit / fee
    let mDepositAndFeeAndTax = mDepositAndFee / tax
    moneyResults.text = "$ " + String(mDepositAndFeeAndTax)

    **} else {
        moneyResults.text = String("Please enter a valid whole number")
    }**