Changing the variable for each array in Java?

Question

I am creating a programme where you convert numbers to roman numbers.

Here is my code:

public static void main(String[] args) {

        System.out.println(convertDigitsToRoman(SplitNumbersIntoDigits(3567)));
    }

    public static int[] SplitNumbersIntoDigits(int numberToConvert) {
        //converting the number into digits
        int[] digit = new int[4];
        digit[0] = numberToConvert / 1000;
        digit[1] = (numberToConvert % 1000) / 100;
        digit[2] = (numberToConvert % 100) / 10;
        digit[3] = numberToConvert % 10;
        return digit;

    }

    public static String convertDigitsToRoman(int[] digit) {
        String a = "I", b = "V", c = "X";


        String allDigitInRoman = "";
        for (int i = 0; i < digit.length; i++) {

            String digitInRoman = "";
            if (digit[i] < 4) {
                for (int j = 0; j < digit[i]; j++) {
                    digitInRoman += a;
                }
            } else if (digit[i] == 4) {
                digitInRoman = String.valueOf(a) + b;
            } else if (digit[i] == 5) {
                digitInRoman = String.valueOf(b);
            } else if (digit[i] > 5 && digit[i] < 9) {
                String plusA = "";
                for (int k = 5; k < digit[i]; k++) {
                    plusA += a;
                }
                digitInRoman = b + plusA;
            } else if (digit[i] == 9) {
                digitInRoman = String.valueOf(a) + c;
            }
            allDigitInRoman += digitInRoman;
        }
        return allDigitInRoman;
    }

}

Now everytime when digit[i] changes I want the String a, b, c to change. How can I try to write such as:

when (digit[0]) change a,b,c to M,C,whateevr
when (digit[1]) change a,b,c to L,,whtevr,,whtevr
when (digit[2]) change a,b,c to X,whtevr,whtevr
when (digit[3]) change a,b,c to I, V, X

I know that is not java, it is English but want to know how is achieved in java.

WJS · Accepted Answer · 2022-10-19 19:02:42Z

There is a much easier way to do this. Just like the decimal system has ones, tens, hundreds, ..., so does the Roman numeral system. Consider the following:

String[] thousands = { "", "M", "MM", "MMM" };
String[] hundreds = { "", "C", "CC", "CCC", "CD",
    "D", "DC", "DCC", "DCCC", "CM" };
String[] tens = { "", "X", "XX", "XXX", "XL", "L",
    "LX", "LXX", "LXXX", "XC" };
String[] ones = { "", "I", "II", "III", "IV", "V",
    "VI", "VII", "VIII", "IX" };
String[][] units = { ones, tens, hundreds,
    thousands };

for (int val : new int[] { 2000, 22, 45, 1986, 554,
    209, 1066, 3888 }) {
    int saveVal = val;
    String roman = "";
    int unit = 0;
    while (val > 0) {
        roman = units[unit][val % 10] + roman;
        val /= 10;
        unit++;
    }
    System.out.printf("%-4d = %s\n", saveVal,
        roman);
}

prints

2000 = MM
22   = XXII
45   = XLV
1986 = MCMLXXXVI
554  = DLIV
209  = CCIX
1066 = MLXVI
3888 = MMMDCCCLXXXVIII

The above simply uses the only allowed symbols.
repeatedly using the remainder (%) operator retrieves the digits from right to left.
So the Roman numeral is built from right to left until the value is zero.

Old Dog Programmer · Accepted Answer · 2022-10-19 23:44:03Z

0

Use a two-dimension array:

    char [][] roman = { {'I','V'}, {'X','L'},{'C','D'},{'M'}};

Note that there is no symbol for 5000, so it will be a problem if you need to convert a number that will be that large.

 int pwr = 4;
 for (int i = 0; i < digit.length; ++i) {
    pwr--;
    String digitInRoman = "";
    if (digit[i] <  4) {
       for (int j = 0; j < digit[i]; j++) {
                digitInRoman += roman[pwr][0];

and so on.

So, for a, use roman [pwr][0], for b, use roman [pwr][1].

This changes the way you handle numbers like 9 (IX), 49 (IL), 40 (XL), and so on. To be more consistent with your current code, you might want to try something like

char [][] roman = { {'I','V','X'}, {'X','L','C'},{'C','D','M'},{'M'}};

That would allow you to use roman[pwr][2] where you have c

edited Oct 19, 2022 at 23:44

answered Oct 19, 2022 at 18:55

Old Dog Programmer

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Comments

Old Dog Programmer · Accepted Answer · 2022-10-20 01:16:22Z

You could add a sequence of if conditions to your code. Or use switch ... case:

  public static String convertDigitsToRoman(int[] digit) {
    String a = "I", b = "V", c = "X";

    String allDigitInRoman = "";
    for (int i = 0; i < digit.length; i++) {

        String digitInRoman = "";
        switch (i) {
            
           case 0: 
              a = "M";  
              b = "";  // ??   
              c = "";  // ??
              break; 
 
           case 1:
              a = "C";
              b = "D";
              c = "M";
              break;

           case 2:
              a = "X";
              b = "L";
              c = "C";
              break;

          case 3:
              a = "I";
              b = "V";
              c = "X";
              break;

         default:
              // Handle error 
               break;
 }
 if (digit[i] < 4) {

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