Prepare function not working!

I have created the HomePwner project and right now I am studying the stack views but the prepare function is not functioning well when I want to perform the segue the signal is aborted I have done every thing according to the book why is that happening?

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For example:

The following code does not print the result. What am I doing wrong? Please help!

// Compute the sum of all positive integers from 1 to N recursively
func sum (_ n:Int) -> Int {
   return n + sum (n-1)

let N = 100
let result = sum (N)
print ("1 + 2 + ...\(N) = ", result)