Unwrapping optionals with guard

The guard statement will only allow further execution within a scope if a test passes, and so is suitable for testing whether binding an optional to a value has succeeded:

guard let id = Int("42") else { return } 
let myID: Int = id 
print(myID) 

The preceding code will print myID to the console, since the downcast succeeded.

Perhaps the most common usage for the guard statement is at the beginning of a function that takes an optional argument:

func printId(int: Int?) 
{ 
  guard let myInt = int else { 
    print(#function, "failed") 
    return  
  } 

  // .. do lot of code with int 
  print(int) 
} 

In the preceding code, we test for the presence of a value, and if there is nil, we print an error and then return immediately from the function. However, if there is a value in the int argument, it is unwrapped, and the rest of the function needs no extra braces, and no further unwrapping and/or testing of the myInt variable.

printId(int: Int("34a")) 

What will this code print?