Retrieve values from an array - get "cannot call value of non-function type String" - swift3

Question

I'm trying to retrieve a value from an array, based on an index parsed from a string of digits. I'm stuck on this error, and the other answers to similar questions in this forum appear to be for more advanced developers (this is my first iOS app).
The app will eventually look up weather reports ("MAFOR" groupings of 5 digits each) from a web site, parse each group and lookup values from arrays for wind direction, speed, forecast period etc using each character.
The playground code is below, appreciate any help on where I am going wrong (look for ***)
//: Playground - noun: a place where people can play
import UIKit
var str = "Hello, playground"
// create array for Forecast Period
let forecastPeriodArray = ["Existing conditions at beginning","3 hours","6 hours","9 hours","12 hours","18 hours","24 hours","48 hours","72 hours","Occasionally"]
// create array for Wind Direction
let windDirectionArray = ["Calm","Northeast","East","Southeast","South","Southwest","West","Northwest","North","Variable"]
// create array for Wind Velocity
let windVelocityArray = ["0-10 knots","11-16 knots","17-21 knots","22-27 knots","28-33 knots","34-40 knots","41-47 knots","48-55 knots","56-63 knots","64-71 knots"]
// create array for Forecast Weather
let forecastWeatherArray = ["Moderate or good visibility (> 3 nm.","Risk of ice accumulation (temp 0C to -5C","Strong risk of ice accumulkation (air temp < -5C)","Mist (visibility 1/2 to 3 nm.)","Fog (visibility less than 1/2 nm.)","Drizzle","Rain","Snow, or rain and snow","Squally weather with or without showers","Thunderstorms"]
// retrieve full MAFOR line of several information groups (this will be pulled from a web site)
var myMaforLineString = "11747 19741 13757 19751 11730 19731 11730 13900 11630 13637"
// split into array components wherever " " is encountered
var myMaforArray = myMaforLineString.components(separatedBy: " ")
let count = myMaforArray.count
print("There are \(count) items in the array")
// Go through each group and parse out the needed digits
for maforGroup in myMaforArray {
print("MAFOR group \(maforGroup)")
// get Forecast Period
var idx = maforGroup.index(maforGroup.startIndex, offsetBy: 1)
var periodInt = maforGroup[idx]
print("periodInt is \(periodInt)")
// *** here is where I am stuck... trying to use the periodInt index value to retrieve the description from the ForecastPeriodArray
var periodDescription = forecastPeriodArray(periodInt)
print("Forecast period = (forecastPeriodArray(periodInt)")
// get Wind Direction
idx = maforGroup.index(maforGroup.startIndex, offsetBy: 2)
var directionInt = maforGroup[idx]
print("directionInt is \(directionInt)")
// get Wind Velocity
idx = maforGroup.index(maforGroup.startIndex, offsetBy: 3)
var velocityInt = maforGroup[idx]
print("velocityInt is \(velocityInt)")
// get Weather Forecast
idx = maforGroup.index(maforGroup.startIndex, offsetBy: 4)
var weatherInt = maforGroup[idx]
print("weatherInt is \(weatherInt)")
}

Answer 1

#shallowThought was close.
You are trying to access an array by its index, therefore use the array[index] notation. But your index has to be of the correct type. forecastPeriodArray[periodInt] therefore does not work since periodInt is not an Int as the name would suggest. Currently it is of type Character which does not make much sense.
What you are probably trying to achieve is convert the character to an integer and use that to access the array:
var periodInt = Int(String(maforGroup[idx]))!
You might want to add error handling for the case when the character does not actually represent an integer.