NumberFormatterDemo.swift

import Foundation

func makeFormatted(price: String) -> String? {
    
    // Convert Input Value To Number
    let inputFormatter = NumberFormatter()
    inputFormatter.locale = Locale(identifier: "en") // if you expect something like '3.14'
    inputFormatter.allowsFloats = true
    
    if let number = inputFormatter.number(from: price) {
        
        // Format Number
        let outputFormatter = NumberFormatter()
        outputFormatter.locale = Locale.current
        outputFormatter.allowsFloats = true
        outputFormatter.minimumFractionDigits = 3
        
        return outputFormatter.string(from: number)
        
    } else {
        print("Error: Unable to convert input value to number.")
        return nil
    }
    
}

makeFormatted(price: "3.14")