Thread: Roman to arabic-----yes, again about this

Originally Posted by Argo_Jeude

But for a numbers like this XXC it doesn't.

That's not a valid Roman number. That should be LXXX.

XXC is not a valid Roman Numeral so what's the problem?

Originally Posted by Mario F.

Roman numerical representation rules are quite simple. When read from right to left, if the next character is "bigger or equal" than the current one, you add, if it is smaller you subtract.

Well, no. Do you represent 1999 as MIM or MCMXCIC? Do you represent 45 as VL, XLV, or XLVX? Roman numerical representation rules are a bit more complex than you've stated.

Well, I've decided to do one.

I'm teaching myself classes and had gone trough strings and iterators before. This looked like a fun thing to put my hands on.

Attached you can find a class that both validates and converts roman numerals to decimal. Probably a rude attempt, by many standards...

I followed on Indigo's teacher set of rules and added a few more. Namely:

• If subtracted before cannot subtract again same or higher (To avoid CMCM and IXCM, instead of MDCCC and CMIX)
• Only allow I, X, C and M to repeat
• Don't allow more than 2 repetitions (CCCC instead of CD)

The class has no default constructor. It has to be initialized with a string. There's no public member functions besides the constructor which validates and converts the string. The class exposes:

valid - bool, returns true if the numeral is a valid roman numeral.

numeral - string, the roman numeral used to initialize the class

arabic - int, the decimal conversion of the numeral if valid is TRUE, or 0 if valid is FALSE. (remember, romans had no zero representation)

Note:
The current rules in the class implementation don't allow for numerals above 3999. Romans had a notation for numbers higher than this. It was composed of the same letters we all know, but with a dash above them. That letter would then become its normal value times 5,000.

So, to represent the number 4000, for instance, they would write:

Code:

 _
MI

Some people repeat M several times to represent numbers above 3999. In order to keep with the historical notation, I didn't allow this on the class. As such, it can only be used for numbers between 1 and 3999.

If you actually go to the trouble of checking this out, let me know where it can be improved.

Well... you didn't understand the code I posted...

You are already doing it. That's what the function you called RimDec() does. It either returns the decimal number represented by the roman literal, or returns 0. You just need to check for 0 to know if the roman number is valid.

As for checking for instances of the same roman literal in sequence, one way is with a counter.

Code:

- Declare an int and initialize it to 0
- Declare an empty char.
- Everytime you read a new roman literal (and starting righ with the first literal):
    - check to see if the literal is == to the char
        - If it is,
            - increment int
            - check if int == 4 (you have 4 roman literals in sequence)
                - If it is, your roman literal is invalid...
        - If it is not,
            - assign 1 to int (in other words reset it)
            - assign the new roman literal to the char
- loop to the next literal

As a side note, your Rim_Dec function is declaring broj, but not using it.

Code:

#include<iostream>
using namespace std;
int Rim_Dec(char a);
int main(){
char RimBr[11],y;
int ArapTemp[10],suma=0,x=0;
cout<<"Please enter roman number: ";
cin>>RimBr;

for(int i=0;i<11;i++){
        if(RimBr[i]=='\0'){
                           break;
                           }
                           if(RimBr[i]==y){
                                           x=x+1;
                                           if(x==4){
                                                    cout<<endl<<"Not right roman number!"<<endl;
                                                    system("pause");
                                                    return 0;
                                                    }
                                           }
        else if(RimBr[i]!=y){
        x=1;
        y=RimBr[i];
        }
}

for(int i=0;i<11;i++){
        ArapTemp[i]=Rim_Dec(RimBr[i]);
        }

for(int i=0;i<11;i++){
        if(ArapTemp[i]=='\0'){
                           break;
                           }
        if(ArapTemp[i]==ArapTemp[i+1]){
                                 if(ArapTemp[i+1]<ArapTemp[i+2]){
                                                           cout<<endl<<"Not right roman number!"<<endl;
                                                           system("pause");
                                                           return 0;
                                                           }
                                 else if(ArapTemp[i+1]==ArapTemp[i+2]){
                                      if(ArapTemp[i+2]<ArapTemp[i+3]){
                                                                cout<<endl<<"Not right roman number!"<<endl;
                                                                system("pause");
                                                                return 0;
                                                                }
                                      }
                                 }
}
for(int i=0;i<11;i++){
        if(ArapTemp[i]>=ArapTemp[i+1]){
                     suma=suma+ArapTemp[i];
                     }
        else if(ArapTemp[i]<ArapTemp[i+1]){
                suma=suma-ArapTemp[i];
                }
}         
cout<<suma<<endl;
system("pause");
return 0;
}
int Rim_Dec(char a){
    int broj;
    switch(a){
              case 'M': broj=1000;
              break;
              case 'D': broj=500;
              break;
              case 'C': broj=100;
              break;
              case 'L': broj=50;
              break;
              case 'X': broj=10;
              break;
              case 'V': broj=5;
              break;
              case 'I': broj=1;
              break;
              default : broj=0;
              }
              return broj;
}

I made checking 'thing' using MarioF's code and I put another code that checks if there is more than one number that is smaller compared to next number in array.
So that we can't enter XXC as 80,but we have to enter LXXX.

But there is one important thing that I needhelp.

XCM I think, should be wrong roman number.
Does anyone knowshow to do it?
Thanx in advance!