Roman into Decimal Program

hira · #1 02-Apr-2008, 20:05

Hello everyone!

I wrote this program which is meant to convert Roman numerals into decimal. I checked a few Roman numerals on it, it does convert CCCLIX to 359 alright but not MCXIV to 1114 (instead the output is 1113) or MDCLXVI to 1666 (the output being 1663). I know there is some logic problem but I can't figure out what. Could anyone please have a look at it?

CPP / C++ / C Code:

#include<iostream>

using namespace std;

class RomanDecimal
{
public:
 void store ();
 void ConvertStore ();
 void print();
 RomanDecimal ();

private:
 char number[8];

 int counter;
};

int main()
{ 
 
 RomanDecimal convert;
 
 cout<<"This is a program to convert Roman numerals into Decimal"<<endl<<endl;

 convert.store ();
 convert.ConvertStore();
 convert.print ();

 return 0;

 

}


void RomanDecimal::store ()
{
 cout<<"Enter in Roman (capital letters)"<<endl;
 cin.getline(number, 8);


}

void RomanDecimal::ConvertStore()
{
	int count=0;
	for (int i=0;i<8;i++)
	{
	  switch(number[i])
  {
  case 'M':count=count+1000;
	  break;
  case 'D':count=count+500;
	  break;
  case 'C':count=count+100;
	  break;
  case 'L':count=count+50;
	  break;
  case 'X':

	  if (number[i-1]='I')

	  count=count+9;
	  else if (number[i+1]='I')
		  count=count+11;

	  break;

  case 'V':

	  if (number[i-1]='I')
		  count=count+4;
	  else if (number[i+1]='I')
		  count=count+6;

	  break;

  case 'I':

	  if ( (number[i-1]='X') || (number[i-1]='V') || (number[i+1]='X') || (number[i+1]='V') )
		  count=count;
	  else
		  count=count+1;


   break;
  };
	}


	counter=count;
}



void RomanDecimal::print()
{
 int c;
 c=counter;

 cout<<"Decimal="<<c<<endl;
}

RomanDecimal::RomanDecimal()
{
	for (int i=0;i<8;i++)
	{
		number[i]='0';

	}

	
	counter=0;
}

mamntc02 · #2 03-Apr-2008, 03:01

Hi,

You have some programming errors:

There's an out of bound error: Imagine you want to get decimal value of 'X', so number="X". When you treat with 'X' in your switch:
CPP / C++ / C Code:
case 'X': if (number[i-1]='I') count=count+9; else if (number[i+1]='I') count=count+11; break;
You are trying to access to number[-1]!!! Out of bounds. You'll have the same problem if length of number is 7 (it can't be 8, because of '\0' character), you'll try to access to number[i+1] = number[8], which is also an error.
Your computation problems are in 'X' and 'V' and 'I'. You always suppose 'X' and 'V' are next to an 'I' character, and that's no always true.
Last error is syntactic: To compare in C++ you must use the operator '==' not '=', which is only to assign.

Just check to convert 'X' or 'V', they give wrong values.

Regards

hira · #3 03-Apr-2008, 09:29

Thanks mamntc!

I have corrected the syntactic errors now, and edited the code to this for X

CPP / C++ / C Code:

case 'X':

      
	  if (number[i-1]=='I')

	  count=count+9;
      
	  else if ( (number[i+1]=='I') && (number[i+2]!='V') )
	  count=count+11;

	  else 
		  
		  count=count+10;
	  

	  break;

and this for V

CPP / C++ / C Code:

case 'V':


	  if ( (number[i-1]=='I') && (number[i-2]=='X') )
		  count=count+4;
	  else if (number[i+1]=='I')
		  count=count+6;
	  else 
		  count=count+5;
	  
	   break;

It gives the numbers correctly, at least the ones I checked. Is it okay now?

How do I correct the out-of-bounds error?

mamntc02 · #4 03-Apr-2008, 10:06

Quote:

Originally Posted by hira

How do I correct the out-of-bounds error?

The easiest way is checking each possible out-of-bounds:

CPP / C++ / C Code:

if (i>0){
	if (number[i-1]=='I')
		count+=9;
}
else if (i < strlen(name)) && {number[i-1]) == 'I')
	count+=11;
	
}
else count+= 10;

Another way could be, overloading [] operator, for example:

CPP / C++ / C Code:

char& operator[](const int i ){
	if (i < 0) return -1; // or thrown an exception
	if (i > strlen(this.name)) return -1;
	
	// rest of code
}

The last possibility is, rather than use a char[8] variable, use a string instance, which is safer using at() member function.

Regards.

hira · #5 03-Apr-2008, 10:24

Thanks once again!

We haven't done operator overloading so I am gonna skip that at the moment.

As for the other code, I am going to try implementing that, though I was wondering if it does calculate okay without (if>0) condition, whats the point of it? The code for number[-1] won't implement in either case (correct me if I am wrong, my concepts aren't too good)

zatora · #6 04-May-2008, 00:27

i have the same problem in my class i am wondering if u have the full solution to the roman--> decimal program, although i get the coding part for the function i am not good at class coding so here is the shortest way to have a conversion function i am assuming that u used a select case for the M=1000,V=5.....

CPP / C++ / C Code:

void convert_roman(int& len,char[] roman,int val[] )
{
// select case codeing part
int i;
for (i=len;i>=1;i--)
    {
        if (roman[len-1]>=roman[len])
            sum = val[len]+val[len-1];
        else
            sum=val[len]-val[len-1];
    }
}

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