Binary operator + cannot be applied to two int operands

Question

Hi I have a question about this code:

1)

let label = "The width is "
let width = 94
let widthLabel = label + String(width)

2)

let height = "3"
let number = 4
let hieghtNumber = number + Int(height)

The first part is working just fine, but I don't get why the second one is not. I am getting the error 'Binary operator "+" cannot be applied to two int operands', which to me does not make much of sense. Can someone help me with some explanation?

See also the answer to this question. Essentially, if A is already declared as a Double of CGFloat or whatever, and B and C are integers, A = B + C will fail with this error message, which obscures the real issue and solution: A = Double(B+C). This question/answer is at the top of the Google search for this error; in some cases the other question's answer may be more helpful. — ConfusionTowers

ABakerSmith ABakerSmith · Accepted Answer · 2015-05-20T12:31:11

1) The first code works because String has an init method that takes an Int. Then on the line

let widthLabel = label + String(width)

You're concatenating the strings, with the + operator, to create widthLabel.

2) Swift error messages can be quite misleading, the actual problem is Int doesn't have a init method that takes a String. In this situation you could use the toInt method on String. Here's an example:

if let h = height.toInt() {
    let heightNumber = number + h
}

You should use and if let statement to check the String can be converted to an Int since toInt will return nil if it fails; force unwrapping in this situation will crash your app. See the following example of what would happen if height wasn't convertible to an Int:

let height = "not a number"

if let h = height.toInt() {
    println(number + h)
} else {
    println("Height wasn't a number")
}

// Prints: Height wasn't a number

Swift 2.0 Update:

Int now has an initialiser which takes an String, making example 2 (see above):

if let h = Int(height) {
    let heightNumber = number + h
}

Binary operator + cannot be applied to two int operands

2 Answers