How to convert Swift 3 output of readLine() to Integer?

Question

Please don't mark as duplicate until you read the whole thing. This is specific to Swift 3.

I have functions that have parameters such as Ints, Floats, etc. I'd like to take the output of readLine() and have Swift accept the output of readLine() as these types, but unfortunately readLine() outputs a String? and when I try to convert it tells me it's not unwrapped. I need help. I'm using Ubuntu 16.04.

For example, if I had area(width: 15, height: 15), how would I replace 15 and 15 with two constants containing readLine() or any equivalent to readLine() to accept input from a user in the terminal?

Also note that the program I am writing is specifically doing math, as most people seem to be happy with strings, this is literally a CLI-based calculator.

EDIT 1 (lol) Okay, here's a more exact explanation of above. The following code will print the area of a trapezoid:

import Foundation

func areaTrapezoid(height: Float, baseOne: Float, baseTwo: Float) {
    let inside = baseOne + baseTwo
    let outside = 0.5 * height
      let result = outside * inside
        print("Area of Trapezoid is \(result)")
  }

areaTrapezoid(height: 10, baseOne: 2, baseTwo: 3)

So, the trapezoid has a height of 10 units, and two bases that have lengths of 2 and 3 respectively. However, I want to do something like:

import Foundation

func areaTrapezoid(height: Float, baseOne: Float, baseTwo: Float) {
    let inside = baseOne + baseTwo
    let outside = 0.5 * height
      let result = outside * inside
        print("Area of Trapezoid is \(result)")
  }

let h = readLine()
areaTrapezoid(height: h, baseOne: 2, baseTwo: 3)

Except, as is already obvious, readLine() will output an optional string, and not a Float. I want the user to be able to input the numbers via CLI in sort of an interactive way, if you will. I'm just learning Swift, but I did something similar in C++ when I was learning that language. Thanks for any help you can provide.

score 5 · Accepted Answer · answered Jul 03 '16 at 07:39

5

readLine() returns an Optional String.

To unwrap the String, you can use if let, and to convert the String to an integer, use Int().

Example:

import Foundation
if let typed = readLine() {
  if let num = Int(typed) {
      print(num)
  }
}

Let's say you prompted the user twice:

let prompt1 = readLine()
let prompt2 = readLine()

Then:

if let response1 = prompt1, 
    response2 = prompt2, 
    num1 = Int(response1), 
    num2 = Int(response2) {
    print("The sum of \(num1) and \(num2) is \(num1 + num2)")
}

answered Jul 03 '16 at 07:39

Eric Aya

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I didn't know I could actually comment! Okay, so see the update. Does this apply there? – M Gage Morgan Jul 03 '16 at 07:45
Yes, all the same. You can use `Float()` or `Double()` the same as I use `Int()` in my example, to convert from the String input. – Eric Aya Jul 03 '16 at 07:47
Tried and true, brother. Thanks, I didn't think there'd be an easy way! – M Gage Morgan Jul 03 '16 at 07:54

How to convert Swift 3 output of readLine() to Integer?

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