Convert Integer to Roman Numeral String in Swift

Roman Numeral Converter In Swift

I did this, which works for 1 to 4999

let initial = 1980
var val = initial
var countForRoman : [(rom: String, num: Int)] = []    // how many occurences of romanNumbers; don't use dictionaries as not ordered

for (index, number) in numberValue.enumerated() {
    let x = val / number
    if x > 0 {
        countForRoman.append((romanNumeral[index], x))
        val = val - x * number
    }
}
print(countForRoman)    // Just to see how it converted

var romanString = ""
for pairs in countForRoman {
    let iter = pairs.num
    for _ in 1 ... iter { romanString += pairs.rom }
}

print(initial, "in roman is", romanString)

Example with 1980:

[(rom: "M", num: 1), (rom: "CM", num: 1), (rom: "L", num: 1), (rom: "X", num: 3)]
1980 in roman is MCMLXXX

If you want to go beyond 4999 (here up to 399 999):

var numberValue = [100_000, 90_000, 50_000, 40_000, 10_000, 9000, 5000, 4000, 1000,900,500,400,100,90,50,40,10,9,5,4,1]
var romanNumeral = [
    "(C)",
    "(X)(C)",
    "(L)",
    "(X)(L)",
    "(X)",
    "M(X)",
    "(V)",
    "M(V)",
    "M",
    "CM",
    "D",
    "CD",
    "C",
    "XC",
    "L",
    "XL",
    "X",
    "IX",
    "V",
    "IV",
    "I"
]

let initial = 9999
var val = initial
var countForRoman : [(rom: String, num: Int)] = []    // how many occurences of romanNumbers; don't use dictionaries as not ordered

for (index, number) in numberValue.enumerated() {
    let x = val / number
    if x > 0 {
        countForRoman.append((romanNumeral[index], x))
        val = val - x * number
    }
}
print(countForRoman)    // Just to see how it converted

var romanString = ""
for pairs in countForRoman {
    let iter = pairs.num
    for _ in 1 ... iter { romanString += pairs.rom }
}

print(initial, "in roman is", romanString)

To get

[(rom: "M(X)", num: 1), (rom: "CM", num: 1), (rom: "XC", num: 1), (rom: "IX", num: 1)]
9999 in roman is M(X)CMXCIX

For 39999

[(rom: "(X)", num: 3), (rom: "M(X)", num: 1), (rom: "CM", num: 1), (rom: "XC", num: 1), (rom: "IX", num: 1)]
39999 in roman is (X)(X)(X)M(X)CMXCIX

For 129_999

[(rom: "(C)", num: 1), (rom: "(X)", num: 2), (rom: "M(X)", num: 1), (rom: "CM", num: 1), (rom: "XC", num: 1), (rom: "IX", num: 1)]
129999 in roman is (C)(X)(X)M(X)CMXCIX

Just encapsulate this code in the convert Function and you get it.

How to convert a roman numeral to an NSNumer

Here are a couple of resources that may help you:

Roman Numbers Convert
-This one is probably the better of the two as this has forward/backward translation

pzearfoss / NSNumber-RomanNumerals
-This is a simple category; however, it only converts NSNumber to Roman Numeral. You may be able to tweak it to go the other way around.

Basic program to convert integer to Roman numerals?

One of the best ways to deal with this is using the divmod function. You check if the given number matches any Roman numeral from the highest to the lowest. At every match, you should return the respective character.

Some numbers will have remainders when you use the modulo function, so you also apply the same logic to the remainder. Obviously, I'm hinting at recursion.

See my answer below. I use an OrderedDict to make sure that I can iterate "downwards" the list, then I use a recursion of divmod to generate matches. Finally, I join all generated answers to produce a string.

from collections import OrderedDict

def write_roman(num):

    roman = OrderedDict()
    roman[1000] = "M"
    roman[900] = "CM"
    roman[500] = "D"
    roman[400] = "CD"
    roman[100] = "C"
    roman[90] = "XC"
    roman[50] = "L"
    roman[40] = "XL"
    roman[10] = "X"
    roman[9] = "IX"
    roman[5] = "V"
    roman[4] = "IV"
    roman[1] = "I"

    def roman_num(num):
        for r in roman.keys():
            x, y = divmod(num, r)
            yield roman[r] * x
            num -= (r * x)
            if num <= 0:
                break

    return "".join([a for a in roman_num(num)])

Taking it for a spin:

num = 35
print write_roman(num)
# XXXV

num = 994
print write_roman(num)
# CMXCIV

num = 1995
print write_roman(num)
# MCMXCV

num = 2015
print write_roman(num)
# MMXV

Convert Int to String in Swift

Converting Int to String:

let x : Int = 42
var myString = String(x)

And the other way around - converting String to Int:

let myString : String = "42"
let x: Int? = myString.toInt()

if (x != nil) {
    // Successfully converted String to Int
}

Or if you're using Swift 2 or 3:

let x: Int? = Int(myString)

Converting Roman Numerals To Decimal

It will be good if you traverse in reverse.

public class RomanToDecimal {
    public static void romanToDecimal(java.lang.String romanNumber) {
        int decimal = 0;
        int lastNumber = 0;
        String romanNumeral = romanNumber.toUpperCase();
        /* operation to be performed on upper cases even if user 
           enters roman values in lower case chars */
        for (int x = romanNumeral.length() - 1; x >= 0 ; x--) {
            char convertToDecimal = romanNumeral.charAt(x);

            switch (convertToDecimal) {
                case 'M':
                    decimal = processDecimal(1000, lastNumber, decimal);
                    lastNumber = 1000;
                    break;

                case 'D':
                    decimal = processDecimal(500, lastNumber, decimal);
                    lastNumber = 500;
                    break;

                case 'C':
                    decimal = processDecimal(100, lastNumber, decimal);
                    lastNumber = 100;
                    break;

                case 'L':
                    decimal = processDecimal(50, lastNumber, decimal);
                    lastNumber = 50;
                    break;

                case 'X':
                    decimal = processDecimal(10, lastNumber, decimal);
                    lastNumber = 10;
                    break;

                case 'V':
                    decimal = processDecimal(5, lastNumber, decimal);
                    lastNumber = 5;
                    break;

                case 'I':
                    decimal = processDecimal(1, lastNumber, decimal);
                    lastNumber = 1;
                    break;
            }
        }
        System.out.println(decimal);
    }

    public static int processDecimal(int decimal, int lastNumber, int lastDecimal) {
        if (lastNumber > decimal) {
            return lastDecimal - decimal;
        } else {
            return lastDecimal + decimal;
        }
    }

    public static void main(java.lang.String args[]) {
        romanToDecimal("XIV");
    }
}

How to convert Decimal to String with two digits after separator?

This should work

extension Decimal {
    var formattedAmount: String? {
        let formatter = NumberFormatter()
        formatter.generatesDecimalNumbers = true
        formatter.minimumFractionDigits = 2
        formatter.maximumFractionDigits = 2
        return formatter.string(from: self as NSDecimalNumber)
    }
}

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