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Integer to Roman Numerals

Boyle11e (3)
Hi. I've made a program to convert an integer to roman numeral. It runs fine for everything until I get to numbers 8 through 1. I'm not sure why the program doesn't want to output the I's properly. Any guidance on this would be much appreciated!

Here is my code for the calculation:

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 string CalcNumeral (int num) 
{
	int M=0; //1000
	int D=0; //500
	int C=0; //100
	int L=0; //50
	int X=0; //10
	int IX=0; //9
	int V=0; //5
	int IV=0;//4
	int I=0; //1
	string numeral;

	while (num >= 1000)	
         {
		num = num - 1000;
		M++;
	}

	if (num > 499 && num < 1000) 	
         {
		num = num - 500;
		D++;
	}

	while ( num >=100) 	
         {
		num = num -100;
		C++;
	}

	if (num > 49 && num < 100) 	
         {
		num = num -50;
		L++;
	}

	while ( num > 9 ) 	
         {
		num = num -10;
		X++;
	}

	if (num == 9)
		num = num-9;
		IX++;


	 if ( num < 9  && num > 4) 	
         {
		num = num -5;
		V++;
	}
	 else if (num == 4)
	{
		num = num - 4;
		IV++;
	}
	 
	 else 
	  { 
		for (int i =0; i < num; i++)
		{
			num = num -1;
			I++;
		}
	}
		
	


	for ( int i = 0; i < M; i++) 		
          numeral = numeral + "M";

	if (D == 1)
	    numeral = numeral + "D";

	for (int i = 0; i < C; i++) 
		numeral = numeral + "C";

	if (L == 1)
		numeral = numeral + "L";

	for ( int i = 0; i < X; i++) 
		numeral = numeral + "X";

	if (IX ==1)
		numeral = numeral + "IX";

	if (V == 1)
		numeral = numeral + "V"; 

	else if (IV == 1)
		numeral = numeral + "IV"; 	

         else 
         {
		for (int i = 0; i < I; i++) 		
	          numeral = numeral + "I";
	}

	return numeral;

}
Last edited on
andywestken (4094)
I think you're program needs a bit more work than just fixing the Is

Driving your function with

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#include <iostream>
#include <iomanip>
#include <string>
using namespace std;

string CalcNumeral (int num);

int main(void)
{
    for(int value = 1; 20 >= value; ++value)
    {
        std::string roman = CalcNumeral(value);
        std::cout << setw(2) << value
                  << " = "
                  << setw(8) << roman << '\n';
    }

    return 0;
}


I get

 1 =      IXI
 2 =      IXI
 3 =     IXII
 4 =     IXIV
 5 =      IXV
 6 =      IXV
 7 =      IXV
 8 =      IXV
 9 =       IX
10 =      XIX
11 =     XIXI
12 =     XIXI
13 =    XIXII
14 =    XIXIV
15 =     XIXV
16 =     XIXV
17 =     XIXV
18 =     XIXV
19 =      XIX
20 =     XXIX

To start with, line 64 in your code looks a bit suspicious?

And so do line 60 and 96

And the loop starting on line 62 : the interaction of the loop index and the num look suspicious, and I'm not sure you need a loop here? (you're decrementing by 1?)

Andy

PS fixing just those places, I now get

 1 =        I
 2 =       II
 3 =      III
 4 =       IV
 5 =        V
 6 =       VI
 7 =      VII
 8 =     VIII
 9 =       IX
10 =        X
11 =       XI
12 =      XII
13 =     XIII
14 =      XIV
15 =       XV
16 =      XVI
17 =     XVII
18 =    XVIII
19 =      XIX
20 =       XX


Last edited on
andywestken (4094)
But the code still needs some work...

I get:

   4 =           IV
  40 =         XXXX
 400 =         CCCC
1444 =  MCCCCXXXXIV

driving with

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#include <iostream>
#include <iomanip>
#include <string>
using namespace std;

string CalcNumeral (int num);

const int values[] = {
    4,
    40,
    400,
    1444 };

const int count = sizeof(values)/sizeof(values[0]);

int main(void)
{
    for(int index = 0; count > index; ++index)
    {
        int value = values[index];
        std::string roman = CalcNumeral(value);
        std::cout << setw(4) << value
                  << " = "
                  << setw(12) << roman << '\n';
    }

    return 0;
}


IV's good, but not XL, CD, or MCDXLIV

Andy

Last edited on
Boyle11e (3)
Alright, I had a feeling that that the looping thing was causing some issues. However can you explain what you are fixing? This isn't for marks or anything but my own curiosity.
andywestken (4094)
line 64

You're missing { }s, to the variable IX is always incremented

line 60 and 96

Neither of these elses is needed (I just removed them)

the loop starting on line 62

The problem is that you are decrementing the termination value at the same time as you're incrementing the index, so they end up meeting halfway.

For example, if num start off as 4, you increment the variable I to 1 and increment i to1 and decrement num to 3, then I=2, i=2, num=2. But now stepping the index to 3 terminates the loop. So you're left with I=2 when you wanted 4.

As the increment is 1 there's no need for this loop. I just replaced it with I = num; (by then, all that's left is the units)

I haven't investigated any further.

Andy
Last edited on
Boyle11e (3)
I fixed these things (prior to your post). Everything is working perfectly now. Thank-you for your help!! I really do appreciate it.
andywestken (4094)
Cool

You could contract your code by making use of arrays. An array of structs would be best, but normal arrays would work, too.
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