Playground execution failed on Int() type conversion

Question

I was working on this tutorial on Swift when I ran into this problem.

code:

var languagesLearned: String = "3"
if let num: Int? = Int(languagesLearned)
{
    print("It is a number")
}
else
{
    print("It is not a number")
}

error:

Playground execution failed: /var/folders/f7/0j8dbxls0kv0l9d6jwk30f2h0000gn/T/lldb/20598/playground134.swift:72:20: error: cannot invoke 'init' with an argument of type '@lvalue String'
if let num: Int? = Int(languagesLearned)
                   ^~~~~~~~~~~~~~~~~~~~~

I can't find anything on why I'm getting this kind of error. I also have no idea what it's saying about init.

Corrected Code After Answer

var languagesLearned: String = "3"
var languagesLearnedNum = languagesLearned.toInt()
if let num = languagesLearnedNum
{
    print("It is a number")
}
else
{
    print("It is not a number")
}

Answer 1

在 Swift 1.x 中，使用：

languagesLearned.toInt()