Converting Integers to Roman Numerals in Java

Question

The homework for my Java class instructs us to take an integer input from the user (up to 3999) and convert it into a Roman Numeral. The trouble I am having with the code is that when I input the integer while testing, it sets the integer to 0 and the Roman Numeral prints out as null. This could be a result of declaring the variables inside an object but im unsure at this point.

public class RomanNumerals
{

    // instance variables

    int input;
    String romanNum;

    /**
     * Object that records the input from a user.
     */
    public RomanNumerals()
    {
        int input=0;
        String romanNum="";

        //System.out.println("Input a number to get a Roman Numeral");
        //int input = integer.nextInt();
    }
    public int Scanner()
    {
        Scanner integer = new Scanner(System.in);
        System.out.println("Input a number to get a Roman Numeral: ");
        int input = integer.nextInt();
        return input;
    }
    /**
     * Object that takes the input from the user and determines what roman numerals are appropriate.
     */
    public String Int2Roman()
    {
        if (input < 1 || input > 3999)
        {
            System.out.println("Please input a number between 1 and 3999.");
        }
        while (input >= 1000)
        {
            romanNum = romanNum + "M";
            input = input - 1000;
        }
        while (input >= 900)
        {
            romanNum = romanNum + "CM";
            input = input - 900;
        }
        while (input >= 500)
        {
            romanNum = romanNum + "S";
            input = input - 500;
        }
        while (input >= 400)
        {
            romanNum = romanNum + "CS";
            input = input - 1000;
        }
        while (input >= 100)
        {
            romanNum = romanNum + "C";
            input = input - 100;
        }
        while (input >= 90)
        {
            romanNum = romanNum + "XC";
            input = input - 1000;
        }
        while (input >= 50)
        {
            romanNum = romanNum + "L";
            input = input - 1000;
        }
        while (input >= 40)
        {
            romanNum = romanNum + "XL";
            input = input - 40;
        }
        while (input >= 10)
        {
            romanNum = romanNum + "X";
            input = input - 10;
        }
        while (input >= 9)
        {
            romanNum = romanNum + "IX";
            input = input - 9;
        }
        while (input >= 5)
        {
            romanNum = romanNum + "V";
            input = input - 5;
        }
        while (input >= 4)
        {
            romanNum = romanNum + "IV";
            input = input - 4;
        }
        while (input >= 1)
        {
            romanNum = romanNum + "I";
            input = input - 5;
        }
        System.out.println("The Roman Numeral of " + input + " is " + romanNum);
        return romanNum;
    }
    public static void main(String[] args)
    {
        RomanNumerals a = new RomanNumerals();
        a.Scanner();
        a.Int2Roman();
    }
}

Answer 1

Your Scanner method does not store the keyboard input in the field (instance variable) input but in a local variable input .

Replace

int input = integer.nextInt(); //this declares a new local variable

with

input = integer.nextInt(); //uses the existing field 

Answer 2

try this to see if works , works for me, simple , basic , pretty straight forward

public static void main(String[] args) {



    //INPUNT INTEGER VALUE
    // OUTPUT STRING VALUE (SYSTEM CONSOLE OUTPUT

    //**********************************************************************************//

    int _inValue = 117; //int parameter value


    //**********************************************************************************//

    //check if the number is between 1 and 3999
    if (_inValue < 1){
        System.out.println("integer can't be less than 1");
        return;
    }
    if (_inValue > 3999){
        System.out.println("integer can't be more than 3999");
        return;
    }

    //convert the value in array to work by separate numbers
    char[] arg = String.valueOf(_inValue).toCharArray();

    //count the number of characters to use a case condition or length of the integer in value
    int _count = Integer.toString(_inValue).length();

    // output variable
    String _output = "";

    //case condition base in the length of the integer value
    switch (_count){
        case 1: // case base in one figure (1)
            switch (_inValue){
                case 1:
                    _output = "I";
                    break;
                case 2:
                    _output = "II";
                    break;
                case 3:
                    _output = "III";
                    break;
                case 4:
                    _output = "IV";
                    break;
                case 5:
                    _output = "V";
                    break;
                case 6:
                    _output = "VI";
                    break;
                case 7:
                    _output = "VII";
                    break;
                case 8:
                    _output = "VIII";
                    break;
                case 9:
                    _output = "IX";
                    break;
            }
            break;
        case 2: //case base in two figures (10)
            switch (Character.getNumericValue(arg[0])){//base in the first character of the integer value lets use another case condition
                case 1:
                    _output = "X";
                    break;
                case 2:
                    _output = "XX";
                    break;
                case 3:
                    _output = "XXX";
                    break;
                case 4:
                    _output = "XL";
                    break;
                case 5:
                    _output = "L";
                    break;
                case 6:
                    _output = "LX";
                    break;
                case 7:
                    _output = "LXX";
                    break;
                case 8:
                    _output = "LXXX";
                    break;
                case 9:
                    _output = "XC";
                    break;
            }
            _output += _getValue10(Character.getNumericValue(arg[1])); //lets call this function to get the other two figures or number to complete the integer amount and build the roman value in string
            break;
        case 3: //case base in three figures (100)
            switch (Character.getNumericValue(arg[0])){ //base in the first character of the integer value lets use another case condition
                case 1:
                    _output = "C";
                    break;
                case 2:
                    _output = "CC";
                    break;
                case 3:
                    _output = "CCC";
                    break;
                case 4:
                    _output = "CD";
                    break;
                case 5:
                    _output = "D";
                    break;
                case 6:
                    _output = "DC";
                    break;
                case 7:
                    _output = "DCC";
                    break;
                case 8:
                    _output = "DCCC";
                    break;
                case 9:
                    _output = "CM";
                    break;
            }
            _output += _getValue100(Character.getNumericValue(arg[1]),Character.getNumericValue(arg[2])); //lets call this function to get the other two figures or number to complete the integer amount and build the roman value in string
            break;
        case 4: // case base in 4 figures (1000)

            if(_inValue != 1000){ // validate the value if its different of a 1000
                // use a cycle to concat the string base of the number of the integer in value
                for (int i = 0; i < Character.getNumericValue(arg[0]);i++ ){
                    _output += "M";
                }
            }else{
                // if its a 1000 use this one and that's it
                _output += "M";
            }
            _output += _getValue1000(Character.getNumericValue(arg[1]),Character.getNumericValue(arg[2]),Character.getNumericValue(arg[3])); //lets call this function to get the other three figures or number to complete the integer amount and build the roman value in string
            break;
    }
    System.out.println("the integer number is: " + _inValue);
    System.out.println("the roman number is: " + _output);

}

///method who return the other three values
private static String _getValue1000(int valueOne, int valueTwo, int valueThree){
    String _output = "";
    if(valueOne != 0){
        switch (valueOne){
            case 1:
                _output += "C";
                break;
            case 2:
                _output += "CC";
                break;
            case 3:
                _output += "CCC";
                break;
            case 4:
                _output += "CD";
                break;
            case 5:
                _output += "D";
                break;
            case 6:
                _output += "DC";
                break;
            case 7:
                _output += "DCC";
                break;
            case 8:
                _output += "DCCC";
                break;
            case 9:
                _output += "CM";
                break;
        }

    }
    if(valueTwo != 0){
        switch (valueTwo){
            case 1:
                _output += "X";
                break;
            case 2:
                _output += "XX";
                break;
            case 3:
                _output += "XXX";
                break;
            case 4:
                _output += "XL";
                break;
            case 5:
                _output += "L";
                break;
            case 6:
                _output += "LX";
                break;
            case 7:
                _output += "LXX";
                break;
            case 8:
                _output += "LXXX";
                break;
            case 9:
                _output += "XC";
                break;
        }
    }
    if(valueThree != 0){
        switch (valueThree){
            case 1:
                _output += "I";
                break;
            case 2:
                _output += "II";
                break;
            case 3:
                _output += "III";
                break;
            case 4:
                _output += "IV";
                break;
            case 5:
                _output += "V";
                break;
            case 6:
                _output += "VI";
                break;
            case 7:
                _output += "VII";
                break;
            case 8:
                _output += "VIII";
                break;
            case 9:
                _output += "IX";
                break;
        }

    }

    return _output;
}

/// method who return the other two values
private static String _getValue100(int valueOne, int valueTwo){
    String _output = "";

    if(valueOne != 0){
        switch (valueOne){
            case 1:
                _output += "X";
                break;
            case 2:
                _output += "XX";
                break;
            case 3:
                _output += "XXX";
                break;
            case 4:
                _output += "XL";
                break;
            case 5:
                _output += "L";
                break;
            case 6:
                _output += "LX";
                break;
            case 7:
                _output += "LXX";
                break;
            case 8:
                _output += "LXXX";
                break;
            case 9:
                _output += "XC";
                break;
        }

    }
    if(valueTwo != 0){
        switch (valueTwo){
            case 1:
                _output += "I";
                break;
            case 2:
                _output += "II";
                break;
            case 3:
                _output += "III";
                break;
            case 4:
                _output += "IV";
                break;
            case 5:
                _output += "V";
                break;
            case 6:
                _output += "VI";
                break;
            case 7:
                _output += "VII";
                break;
            case 8:
                _output += "VIII";
                break;
            case 9:
                _output += "IX";
                break;
        }

    }

    return _output;
}

/// method who return one other value
private static String _getValue10(int valueOne){
    String _output = "";

    if(valueOne != 0){
        switch (valueOne){
            case 1:
                _output += "I";
                break;
            case 2:
                _output += "II";
                break;
            case 3:
                _output += "III";
                break;
            case 4:
                _output += "IV";
                break;
            case 5:
                _output += "V";
                break;
            case 6:
                _output += "VI";
                break;
            case 7:
                _output += "VII";
                break;
            case 8:
                _output += "VIII";
                break;
            case 9:
                _output += "IX";
                break;
        }

    }

    return _output;
}