swift - unexpectedly found nil while unwrapping an Optional value, when trying to cover toInt() -

i new in swift , trying build simple program converts number of week in days, minutes , seconds, cannot convert string int. when thought done using toint(), message appeared in line:

var tempoemdias:int! = timeindays.text.toint(),

fatal error: unexpectedly found nil while unwrapping optional value... 

does can me? code below...

import uikit  class viewcontroller: uiviewcontroller {  @iboutlet var timeindays: uitextfield!  @iboutlet var numberofweeks: uilabel!   @iboutlet var numberofhours: uilabel!   @iboutlet var numberofminutes: uilabel!   @iboutlet var numberofseconds: uilabel!   @ibaction func calculatempo(sender: anyobject) {    // below: fatal error: unexpectedly found nil while unwrapping optional value.      var tempoemdias:int! = timeindays.text.toint()        // calcula semana      var numerodesemanas:int = 0       if tempoemdias! <= 7 {         numerodesemanas = 1     } else {      numerodesemanas = tempoemdias! / 7      }      let numerodesemanascerto:int = int(numerodesemanas)      numberofweeks.text = "/(numerodesemanascerto) semanas"      // calcula horas      let numerodehoras = numerodesemanascerto * 24     numberofhours.text = "/(numerodehoras) horas"      // calcula minutos      let numerodeminutos = numerodehoras * 60     numberofminutes.text = "/(numerodeminutos) minutos"      // calcula segundos      let numerodesegundos = numerodeminutos * 60     numberofseconds.text = "/(numerodesegundos) segundos"  } 

you error because toint() returns optional integer value , trying assign non-optional tempoemdias.

from documentation:

toint()  use method convert string integer value. method returns optional integer value (int?)—if conversion succeeds, value resulting integer; if conversion fails, value nil:  let string = "42" if let number = string.toint() {     println("got number: \(number)") } else {     println("couldn't convert number") } // prints "got number: 42"