How to add days to a date in swift 3

I am getting number of days,Start date and end date from a service. I want to get the list of all dates in between start date and end date. Let's say my start date is 2017/08/15 and end date is 2017/08/16 and number of days is 2.

But I am getting the date list like this.

##### CONVERTED STRING DATE 2017-08-16

##### CONVERTED STRING DATE  2017-08-17

##### CONVERTED STRING DATE 2017-08-18

And I have another date like this

Start date 2017/08/23 end date 2017/09/01 and number of days 8. then I get the list like this.

##### CONVERTED STRING DATE  2017-08-24

##### CONVERTED STRING DATE  2017-08-25

##### CONVERTED STRING DATE  2017-08-28

##### CONVERTED STRING DATE  2017-08-29

##### CONVERTED STRING DATE  2017-08-30

##### CONVERTED STRING DATE  2017-08-31


##### CONVERTED STRING DATE  2017-09-01

This is how I get the dates array

 numberOfDates=Int(ceil(numOfDay))
                        //numberOfDates=numberOfDates-1
                        let arrayDates=self.generateDates(startDate: startDate, addbyUnit: .day, value: numberOfDates)

This is how my date calculation method

internal func generateDates(startDate :Date?, addbyUnit:Calendar.Component, value : Int) -> [Date]
{
    //print("####START DATE#######\(startDate)")
    var calendar = Calendar.current
    calendar.timeZone=TimeZone.current
    var datesArray: [Date] =  [Date] ()

    for i in 0 ... value {
        var addAmount:Int!
        if(value==0)
        {
            addAmount=0
        }
        else
        {
            addAmount=1
        }
        if let newDate = calendar.date(byAdding: addbyUnit, value: i + addAmount, to: startDate!) {

            let strDayName=self.getDayName(mydate: newDate)
            if (strDayName != "Saturday" && strDayName != "Sunday")
            {
                datesArray.append(newDate)
            }

        }
    }

    return datesArray
}

My problem is sometimes the date list is wrong (1st scenario) but its correct in the 2nd scenario.