在Swift中将变量声明为Integer

Question

So I'm trying to learn swift and on button action, I want to declare a variable as an integer that collects the value from a text field, calculates if it is not nil and prints the value. Why is it asking me to make the variable constant?

This what I've tried

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var enterAge: UITextField!
    @IBOutlet weak var catAge: UILabel!

    @IBAction func findAge(sender: AnyObject) {

        var newage = Int(enterAge.text!)

        if newage! == 0
        {

       var catyears = newage! * 7
        catAge.text = "Your cat is \(catyears) in age"
        }

        else
        {

            catAge.text = "Please enter a whole number"
        }

    }
        override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

Xcode version 7.1 The error:

Thanks

Answer 1

It is a warning , not an error: your program will still compile and run even if you ignore it (but down the road, it's best practice if you don't).

It is telling you that because your 'variable' gets assigned its initial and only value once, and thereafter it is only read from (never written to). Hence, it doesn't need to be a variable; a constant will do (and better reflects the intent of your program).

Answer 2

var - allows you to change the value of the object or variable created after assignment,

where,

let is constant and can be initialised only once. your snippet show us you are using your variable to just store the value got from textfield and never changed later there after, consider your requirement and usage system is advising you to change your variable to constant. changing variable to constant will not effect you code.

if you want to check then just write

newage = newage + 0

this will result same but see the warning is gone now, we are assigning/changing the value of variable.

hope this explains why you are getting the warning..