Better way to check for a Int in a textbox - ios

Question

I am learning Xcode and creating a very simply program with a textbox(txt box) in which the user enters a value, a button (btnCalc) that performs a calculation, and a label (lblcalcdnumber) that shows the calc'd number. I have already selected Number Pad to be displayed as the dropdown keyboard but i want to check to make sure that if they enter anything other than a number that nothing happens. The code i have works but i feel like there should be a cleaner solution. Essential i want them to only enter Integers in the textbook.
// Mark: Actions
#IBAction func btnCalc(sender: UIButton) {
// let txtbox text beome int
let number1 = Int(txtBox.text!)
// let possibleInt convert mystring to int to check for nil, txtbox becomes OPTIONAL
let possibleInt = Int(txtBox.text!)
let number = 25
if possibleInt != nil {
let combinednumber = "\(Int(number1!) * number)"
lblCalcedNumber.text = combinednumber
}
else {
txtBox.text = ""
txtBox.placeholder = "Please Enter a Valid Number"
}
}

Answer 1

You can use if and let together to create an optional. If the value is not nil it will cast to possibleInt, otherwise, it will evaluate as false.
#IBAction func btnCalc(sender: UIButton) {
if let possibleInt = Int(txtBox.text!) {
let combinednumber = "\(possibleInt * 25)"
lblCalcedNumber.text = combinednumber
}
else {
txtBox.text = ""
txtBox.placeholder = "Please Enter a Valid Number"
}
}

Answer 2

Your variables 'number1' and 'possibleInt' have the same value, so you only need one of them for this section of code. Since 'number' is only used once it would be better to use the value itself rather than create a variable for it, however, if you use it elsewhere keep it as a variable so you only need to change your code in one spot. If you weren't using the possibleInt/number1 value inside the if statement, you could be even more efficient by doing if Int(txtBox.text!) != nil. Try this:
// Mark: Actions
#IBAction func btnCalc(sender: UIButton) {
let possibleInt = Int(txtBox.text!)
if possibleInt != nil {
let combinednumber = "\(possibleInt * 25)"
lblCalcedNumber.text = combinednumber
}
else {
txtBox.text = ""
txtBox.placeholder = "Please Enter a Valid Number"
}
}