Swift: error: linker command failed with exit code 1

There are similar questions, but none that answer my question.

I am using Swift 2.0 I am working on a project that shows longitude and latitude using CoreLocation.

I also am using the Social framework to post to twitter and facebook.

I am getting an error that says "error: linker command failed with exit code 1 " and then it tells me "(use -v to see invocation)" but I do not understand that.

I am going off an answer here on SO to write the location services portion. here is the link http://stackoverflow.com/a/24696878/6140339

here is my code:

import UIKit
import Social
import CoreLocation

@UIApplicationMain

class FirstViewController: UIViewController, CLLocationManagerDelegate, UIApplicationDelegate {


var window: UIWindow?
var locationManager: CLLocationManager!
var seenError : Bool = false
var locationFixAchieved: Bool = false
var locationStatus : NSString = "Not Started"

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject : AnyObject]?) -> Bool {
    initLocationManager();
    return true
}

func initLocationManager() {
    seenError = false
    locationFixAchieved = false
    locationManager = CLLocationManager()
    locationManager.delegate = self
    CLLocationManager.locationServicesEnabled()
    locationManager.desiredAccuracy = kCLLocationAccuracyBest

    locationManager.requestAlwaysAuthorization()
}

func locationManager(manager: CLLocationManager, didFailWithError error: NSError) {
    locationManager.stopUpdatingLocation()
    if (error == true) {
        if (seenError == false) {
            seenError = true
            print(error)
        }
    }
}

func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
    if (locationFixAchieved == false) {
        locationFixAchieved = true
        let locationArray = locations as NSArray
        let locationObj = locationArray.lastObject as! CLLocation
        let coord = locationObj.coordinate

        print(coord.latitude)
        print(coord.longitude)
    }
}

func locationManager(manager: CLLocationManager, didChangeAuthorizationStatus status: CLAuthorizationStatus) {
    var shouldIAllow = false

    switch status {
    case CLAuthorizationStatus.Restricted:
        locationStatus = "Restricted Access to location"
    case CLAuthorizationStatus.Denied:
        locationStatus = "User denied access to location"
    case CLAuthorizationStatus.NotDetermined:
        locationStatus = "Status not determined"
    default:
        locationStatus = "Allowed to location Access"
        shouldIAllow = true
    }
    NSNotificationCenter.defaultCenter().postNotificationName("LabelHasBeenUpdated", object: nil)
    if (shouldIAllow == true) {
        NSLog("Location to Allowed")
        //Start location services
        locationManager.startUpdatingLocation()
    } else {
        NSLog("Denied access: (locationStatus)")
    }
}



@IBAction func postToFacebookButton(sender: UIButton) {
    if(SLComposeViewController.isAvailableForServiceType(SLServiceTypeFacebook)){
        let socialController = SLComposeViewController(forServiceType: SLServiceTypeFacebook)
        //creates post with pre-desired text
        socialController.setInitialText("")

        self.presentViewController(socialController, animated: true, completion: nil)
    }
}


@IBAction func postTweetButton(sender: UIButton) {
    if(SLComposeViewController.isAvailableForServiceType(SLServiceTypeTwitter)){
        let socialController = SLComposeViewController(forServiceType: SLServiceTypeTwitter)
        //creates post with pre-desired text
        socialController.setInitialText("")

        self.presentViewController(socialController, animated: true, completion: nil)
    }
}

override func preferredStatusBarStyle() -> UIStatusBarStyle {
    return .LightContent
}

override func viewDidLoad() {
    super.viewDidLoad()
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

//layer.cornerRadius layer.cornerRadius

}

Entire error message:

duplicate symbol _main in: /Users/user/Library/Developer/Xcode/DerivedData/FarOut-ekrxzlgzfahpruavmlhyhiwiynum/Build/Intermediates/FarOut.build/Debug-iphonesimulator/FarOut.build/Objects-normal/x86_64/AppDelegate.o /Users/user/Library/Developer/Xcode/DerivedData/FarOut-ekrxzlgzfahpruavmlhyhiwiynum/Build/Intermediates/FarOut.build/Debug-iphonesimulator/FarOut.build/Objects-normal/x86_64/FirstViewController.o ld: 1 duplicate symbol for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)