Basic program to convert Roman number Arabic form? - c++

Question

I am wanting some help in answering these two questions. The first one is this:
I am trying to write a program that converts a single Roman number in the range I (1) to IX (9) to Arabic form. The
program should read a single string from standard input and print the corresponding value to standard output.
I then want to Extend the program so that it works correctly when the input consists of either lower case or upper case Roman letters.
The simplest approach is to convert each character in the input word into uppercase before trying to find a match. Run a
loop over the characters in the string using the index operator ([]) to access each character and use the toupper
function (you will need to include the cctype header file) to get the corresponding uppercase value.
For the second question this is what it wants me to do next:
Extend the program so that it can deal with single digit numbers of any value. A single digit number is one that consists
only of thousands, hundreds, tens, or units. Thus LXX (70) and CD (400) are single digit numbers, but XIV (14) and
MC (1100) are not. Use the same approach as for units digits, but with 4 different arrays, one each for the thousands,
hundreds, tens, and units digits. Try looking for thousands digits first, then for hundreds, and so on. When you find a
match in one of the arrays, print the corresponding value and stop.
Modify the program so that it reads and converts all input numbers until end of file (eof) on standard input. You will
probably be able to do this by simply adding an appropriate reading loop around the code that reads a single line.
Currently this is what i have to start but am unsure how to write a program like this:
#include <iostream>
#include <string>
#include <stdexcept>
using namespace std;
class RomanNumeral
{
public:
const static int M = 1000;
const static int D = 500;
const static int C = 100;
const static int L = 50;
const static int X = 10;
const static int V = 5;
const static int I = 1;
RomanNumeral( const int arabic ) :
m_roman( "" ),
m_arabic( ((arabic > 0) ? arabic : 0) )
{
if( arabic > 0 )
{
int i = arabic;
while( i > 0 )
{
if( ( i - M ) >= 0 )
{
m_roman += "M";
i -= M;
continue;
}
if( ( i - D ) >= 0 )
{
m_roman += "D";
i -= D;
continue;
}
if( ( i - C ) >= 0 )
{
m_roman += "C";
i -= C;
continue;
}
if( ( i - L ) >= 0 )
{
m_roman += "L";
i -= L;
continue;
}
if( ( i - X ) >= 0 )
{
m_roman += "X";
i -= X;
continue;
}
if( ( i - V ) >= 0 )
{
m_roman += "V";
i -= V;
continue;
}
if( ( i - I ) >= 0 )
{
m_roman += "I";
i -= I;
continue;
}
}
}
else
{
m_roman = "0";
}
}
RomanNumeral( const std::string& string ) :
m_roman( ((string.size() > 0 ) ? string : "0" ) ),
m_arabic( 0 )
{
int i = 0;
while( i < (int)string.size() )
{
char c = string[i++];
switch( c )
{
case 'M':
case 'm':
m_arabic += M;
break;
case 'D':
case 'd':
m_arabic += D;
break;
case 'C':
case 'c':
m_arabic += C;
break;
case 'L':
case 'l':
m_arabic += L;
break;
case 'X':
case 'x':
m_arabic += X;
break;
case 'V':
case 'v':
m_arabic += V;
break;
case 'I':
case 'i':
m_arabic += I;
break;
default:
throw new std::out_of_range( "Not a valid Roman numeral!" );
break;
}
}
}
int getArabic()
{
return m_arabic;
}
void setArabic( const int arabic );
const std::string& getRoman()
{
return m_roman;
}
protected:
std::string m_roman;
int m_arabic;
};
int main()
{
std::string roman;
cin >> roman;
try
{
RomanNumeral rn( roman );
cout << rn.getArabic() << endl;
}
catch( exception* ex )
{
cout << roman << " " << ex->what() << endl;
}
return 0;
}
Have been doing some tutorials on it but came across this question on a website the other day but I can't find the solution to this to see how its done. Could you demonstrate how to write a program like this by any chance?

Answer 1

Whenever you're stuck on a problem, try to decompose it into steps and implementing the things you can.
Step one is reading a single word:
std::string word;
std::cin >> word;
Step two is converting the word into a number:
int convert_to_number(const std::string& w) {
if (w == "I") return 1;
if (w == "II") return 2;
// and so on.
}
Step three is doing the conversion and printing the result:
std::cout << convert_to_number(word) << std::endl;
Instead of writing large amounts of if statements, you may want to try using an std::map<std::string, int> or std::unordered_hash<std::string, int> for a constant-time lookup.