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Thread: Roman Numbers

  1. #1
    Java kindergarten chronoz13's Avatar
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    Default Roman Numbers

    help here pls.. i'm having problem on how can i conver a roman number into a real number

    heres what i've got so far
    public class RomanNumbers {
     
        private static BufferedReader br = new BufferedReader(new InputStreamReader(
                                           System.in));
     
        public static void main(String[] args) throws IOException {
     
            char temp = 0;
     
            int rN = 0;
     
            int num = 0;
     
            System.out.print("Enter The Roman Number: ");
            String romanNumber = br.readLine();
     
            for (int count = 0; count <= romanNumber.length() - 1; count++) {
     
                temp = romanNumber.charAt(count);
     
                switch (temp) {
     
                    case 'I':
     
                        rN = 1;
     
                        break;
     
                    case 'V':
     
                        rN = 5;
     
                        break;
                }
     
                num = num + rN;
            }
     
            System.out.println(num);
        }
    }

    the problem is when i enetered a roman number for example:

    IV = 4, because I is less than V which is one of the rules in converting a roman number

    if the first number is less than the next one... it should be subtracted... otherwise it will be added...


    my problem is how can i compare the first value of the roman number into the value next to it..


    i dont have any more problems when the sequence is greatest to least.. because i only have to add the values,,
    but im having a hard time thinking of how could i compare the values to get the answer if the first number is less than the next number


  2. #2
    Senile Half-Wit Freaky Chris's Avatar
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    Default Re: Roman Numbers

    How abou tthis

    import java.util.Scanner;
     
     
    public class Roman {
    	public static void main(String[] args) {
    		Scanner stdIn = new Scanner(System.in);
     
    		System.out.print("Enter a Roman Number:> ");
    		char[] roman = stdIn.nextLine().toCharArray();
     
    		int total = 0;
    		for(int i = roman.length-1; i > -1; i--){
    			switch(roman[i]){
    				case 'I':
    					total += value(roman[i]); break;
    				case 'V':
    				case 'X':
    				case 'L':
    				case 'C':
    				case 'D':
    				case 'M':
    					if(i != 0 && (value(roman[i-1]) < value(roman[i]))){
    						total += value(roman[i]) - value(roman[i-1]);
    						i--;
    					}else{
    						total += value(roman[i]);
    					}
    					break;
    			}
    		}
    		System.out.println(total);
    	}
     
    	public static int value(char c){
    		switch(c){
    			case 'I':
    				return 1;
    			case 'V':
    				return 5;
    			case 'X':
    				return 10;
    			case 'L':
    				return 50;
    			case 'C':
    				return 100;
    			case 'D':
    				return 500;
    			case 'M':
    				return 1000;
    			default:
    				return 0;
    		}
    	}
     
    }

    Chris
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

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    chronoz13 (December 8th, 2009)

  4. #3
    Super Moderator Json's Avatar
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    Default Re: Roman Numbers

    Basically what happens here is that for every character you translate you need to check the next character to see if its bigger than the current character and if it is you know that its a subtraction.

    Read the section called "Subtractive principle" on Roman numerals - Wikipedia, the free encyclopedia

    Generally, Roman numerals are written in descending order from left to right, and are added sequentially, for example MMVI (2006) is interpreted as 1000 + 1000 + 5 + 1.
    Certain combinations employ a subtractive principle, which specifies that where a symbol of smaller value precedes a symbol of larger value, the smaller value is subtracted from the larger value, and the result is added to the total. For example, in MCMXLIV (1944), the symbols C, X and I each precede a symbol of higher value, and the result is interpreted as 1000 plus (1000 minus 100) plus (50 minus 10) plus (5 minus 1).
    A numeral for 10n (I, X, or C) may not precede a numeral larger than 10n+1, where n is an integer.[citation needed] That is, I may precede V and X, but not L or C; X may precede L or C, but not D or M. The numerals 510n (V, L, or D) may not be followed by a numeral of greater or equal value.[citation needed] Any symbol that appears more than once consecutively may not be followed by a symbol of larger value.
    // Json

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    chronoz13 (December 8th, 2009)

  6. #4
    Java kindergarten chronoz13's Avatar
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    Default Re: Roman Numbers

    chris.. i noticed something in the for statement.... the "length" method , i looks different..
    in my IDE (netbeans) it is color green..


    and color green, statnds for fields or objects... but i dont know where that "length" came from...

  7. #5
    Senile Half-Wit Freaky Chris's Avatar
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    Default Re: Roman Numbers

    the variable roman is a char Array, in Java these have a variable known as length containing the size of the array.

    Chris
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

  8. #6
    Java kindergarten chronoz13's Avatar
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    Default Re: Roman Numbers

    ahh so thats it.. a method that returns a length of an array of characters.....

    tnx!!

  9. #7
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    Default Re: Roman Numbers

    Not a method, an instance variable
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

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    Java kindergarten chronoz13's Avatar
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    Default Re: Roman Numbers

    aw .. sorry....

  11. #9
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    Default Re: Roman Numbers

    Just making sure you now

    Chris
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

  12. #10
    Java kindergarten chronoz13's Avatar
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    Default Re: Roman Numbers

    tnx tnx!

  13. #11
    Java kindergarten chronoz13's Avatar
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    Default Re: Roman Numbers

    chris ... just want to ask something about this part...

    			case 'V':
    				case 'X':
    				case 'L':
    				case 'C':
    				case 'D':
    				case 'M':

    ahmm...

    if i pass the characer for example 'V' to the method .value(<char>),
    its doest not return ALL the succeding values after the 'V' right?

    the return value will just depend on the character that i will pass to that method...?

    does my analyzation ryt?


    coz im a bit confuse on my first look on your code...

    i thought it's just an ordinary sequence of switch... (because i dont see a 'break' statement)

    so i thought it will return all the next values after the character that i passed....


    sorry for bad english......

  14. #12
    Super Moderator Json's Avatar
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    Default Re: Roman Numbers

    Basically what happens here is that if you pass in 'V' it will fall through down to the 'M' case and run that code, the same thing happens if you pass in either 'X', 'L', 'C' or 'D'.

    You need to take note that switch cases falls through to the next one unless the case has a call to break in it.

    		switch(roman[i]){
    				case 'I':
    					total += value(roman[i]); break; // We call break here to break out of the switch
    				case 'V': // No break so fall down to X
    				case 'X': // No break so fall down to L
    				case 'L': // No break so fall down to C
    				case 'C': // No break so fall down to D
    				case 'D': // No break so fall down to M
    				case 'M':
    					if(i != 0 && (value(roman[i-1]) < value(roman[i]))){
    						total += value(roman[i]) - value(roman[i-1]);
    						i--;
    					}else{
    						total += value(roman[i]);
    					}
    					break; // BREAK
    			}

    // Json

  15. #13
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    Default Re: Roman Numbers

    what do you mean by 'fall down' sir?

    does it mean it also returns value ? ryt?

    in this case... we are only asking for the value of 'V' ... so the value of the rest are not used....

    am i ryt sir?

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    Super Moderator helloworld922's Avatar
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    Default Re: Roman Numbers

    The next case statement doesn't stop execution of the previous case statement. So, when he says "fall down", he wants all the code from V...M to all be the same.

    char c = 'a';
    switch(c)
    {
    case 'a':
         System.out.println("The char is definitely an a");
    case 'b':
         System.out.println("The char is either an a or  b");
    }

    This will print out:

    The char is definitely an a
    The char is either an a or b

    If we take out the first print statement,
    switch(c)
    {
    case 'a':
    case 'b':
         System.out.println("The char is either an a or  b");
    }

    It will only print out:

    The char is either an a or b

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    chronoz13 (December 9th, 2009)

  18. #15
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    Default Re: Roman Numbers

    pls check this part please
    public class RomanNumbers3 {
     
        private static BufferedReader br = new BufferedReader(new InputStreamReader(
                                           System.in));
     
        public static void main(String[] args) throws IOException {
     
            int rN = 0;
            int equivalent = 0;
            int[] value;
     
            char[] romanChar = {'I'};
     
            System.out.print("Enter a roman number: ");
            String romanNumber = br.readLine();
     
            value = new int[romanNumber.length()];
            romanChar = new char[romanNumber.length()];
     
            // get the values of each of the roman character
            for (int x = romanNumber.length() - 1; x >= 0; x--) {
     
                switch (romanNumber.charAt(x)) {
     
                    case 'I':
     
                        rN = 1;
                        break;
     
                    case 'V':
     
                        rN = 5;
                        break;
     
                    case 'X':
     
                        rN = 10;
                        break;
     
                    case 'L':
     
                        rN = 50;
                        break;
     
                    case 'C':
     
                        rN = 100;
                        break;
     
                    case 'D':
     
                        rN = 500;
                        break;
     
                    case 'M':
     
                        rN = 1000;
                        break;
     
                    default:
     
                        System.out.println("Invalid Roman Character Sequence");
                        break;
                }
     
                // IM HAVING SOME PROBLEM WITH CHECKING OF THE CHARACTERS
                for (int check = romanChar.length - 1; check >= 0; check--) {
     
                    if (romanNumber.charAt(x) != romanChar[0]) {
     
                        System.out.println("WRONG CHARACTER");
                    }
                }
     
                // assign the value according to the sequence of the characters
                value[x] = rN;
            }
     
            for (int n = romanNumber.length() - 1; n >= 0; n--) {
     
                // compute the values according to the sequence of roman characters
                if ((n != 0) && (value[n] > value[n - 1])) {
     
                    equivalent = equivalent + (value[n] - value[n - 1]);
                    n--;
                }
                else {
     
                    equivalent = equivalent + value[n];
                }
            }
     
            System.out.println(equivalent);
        }
    }

    if i entered 'I' it still displays "WRONG CHARACTER"..when the character in the romanChar[] array has a character 'I' in its index(0) why?,.,.... cant figure it out... please help

    what i want here now is to check if there is/ are any illegal character.. so i will display an output for that..
    Last edited by chronoz13; December 12th, 2009 at 01:23 AM.

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