C++ Arabic to roman numeral converter - of input validation loops - c++

Question

The purpose of this program is to take an input of an arabic number and return the equivelant roman numeral. it needs to reject input less than 0 and greater than 3999, but also end on an input of ANY NEGATIVE NUMBER. Also needs an input fail catch for entering a letter instead of an integer. (completely clueless on this part?!)
My question is what order should these conditional statement be in so that the program doesnt just return invalid input for a negative number, it ends the program.
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
string convert(int digit, string low, string mid, string high);
int main()
{
const int MAX_INPUT = 3999, MIN_INPUT = 0, // These constants hold high and low integer numbers,
ARRAY_SIZE = 4; // and the array size declarator.
string answers[ARRAY_SIZE] = { "", "", "", "" }; //An array of string to hold the output from the convert function.
int accumulator = 0; // Variable to hold number of arabic numbers converted.
int userNum = 0;
do {
cout << "Enter a negative number to end the program.\n";
cout << "Enter an arabic number between 1 and 3999: ";
cin >> userNum;;
if (userNum < 0)
{
cout << "Exiting program:";
break;
while (userNum <= MIN_INPUT || userNum >= MAX_INPUT)
{
cout << "\nInvalid Value. Number must be between 1 and 3999: ";
cin >> userNum;
}
}
int thous = userNum / 1000;
cout << thous;
int hund = userNum % 1000 / 100;
cout << "hundreds:" << hund;
int tens = userNum % 100 / 10;
cout << "tens:" << tens;
int ones = userNum % 10 / 1;
cout << "Ones: " << ones << endl;
answers[0] = convert(thous, "M", "M", "M");
answers[1] = convert(hund, "C", "D", "M");
answers[2] = convert(tens, "X", "L", "C");
answers[3] = convert(ones, "I", "V", "X");
cout << answers[0] << endl << answers[1] << endl << answers[2];
cout << endl << answers[3] << endl;
} while (userNum > 0);
system("PAUSE");
return 0;
}
string convert(int digit, string low, string mid, string high)
{
cout << digit << endl;
if (digit == 1)
{
return low;
}
if (digit == 2)
{
return low + low;
}
if (digit == 3)
{
return low + low + low;
}
if (digit == 4)
{
return low + mid;
}
if (digit == 5)
{
return mid;
}
if (digit == 6)
{
return mid + low;
}
if (digit == 7)
{
return mid + low + low;
}
if (digit == 8)
{
return mid + low + low + low;
}
if (digit == 9)
{
return low + high;
}
if (digit == 0)
{
return "";
}
}

Answer 1

A possible solution with minimal refactoring of your current code:
int main()
{
const int MAX_INPUT = 3999, MIN_INPUT = 0, // These constants hold high and low integer numbers,
ARRAY_SIZE = 4; // and the array size declarator.
string answers[ARRAY_SIZE] = { "", "", "", "" }; //An array of string to hold the output from the convert function.
int accumulator = 0; // Variable to hold number of arabic numbers converted.
int userNum = 0;
do {
cout << "Enter a negative number to end the program.\n";
cout << "Enter an arabic number between 1 and 3999: ";
//cin >> userNum;;
while(!(cin >> userNum) || (userNum < 1 || userNum > 3999)){
if (userNum < 0)
{
cout << "Exiting program:";
return 0;
} else {
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
cout << "\nInvalid Value. Number must be between 1 and 3999. Try again ";
}
}
int thous = userNum / 1000;
cout << thous;
int hund = userNum % 1000 / 100;
cout << "hundreds:" << hund;
int tens = userNum % 100 / 10;
cout << "tens:" << tens;
int ones = userNum % 10 / 1;
cout << "Ones: " << ones << endl;
answers[0] = convert(thous, "M", "M", "M");
answers[1] = convert(hund, "C", "D", "M");
answers[2] = convert(tens, "X", "L", "C");
answers[3] = convert(ones, "I", "V", "X");
cout << answers[0] << endl << answers[1] << endl << answers[2];
cout << endl << answers[3] << endl;
} while (userNum > 0);
system("PAUSE");
return 0;
}

Answer 2

In sudo code:
while (inputVar >= 0) {
try {
inputVar = stoi(inputVar)
} catch {
print("Input error")
}
if in range(min to max) {
roman = romanEquiv(inputVar)
print(roman)
} else {
print("Invalid entry.")
}
}
Try-catch blocks (for catching exceptions you know your program should handle)
std::stoi a function in the cpp library to try and convert a string to an integer
Hope this helps, let me know how it goes.

Answer 3

I revised the beginning of the main method and the beginning of the while loop.
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
#define MAX_INPUT 3999 // These constants hold high and low integer numbers,
#define MIN_INPUT 1
#define ARRAY_SIZE 4 // and the array size declarator.
string convert(int digit, string low, string mid, string high);
int main()
{
string answers[ARRAY_SIZE] = { "", "", "", "" }; //An array of string to hold the output from the convert function.
int accumulator = 0; // Variable to hold number of arabic numbers converted.
int userNum = 0;
string strUserNum;
do {
cout << "Enter a negative number to end the program.\n";
cout << "Enter an arabic number between 1 and 3999: ";
cin >> strUserNum;
userNum = std::stoi(strUserNum);
if (userNum == 0 || userNum > MAX_INPUT)
{
cout << "\nInvalid Value. Number must be between 1 and 3999: " << endl;
continue;
}
else if (userNum < MIN_INPUT)
{
cout << "Exiting program:";
break;
}
int thous = userNum / 1000;
cout << "thousands: " << thous;
int hund = userNum % 1000 / 100;
cout << " hundreds: " << hund;
int tens = userNum % 100 / 10;
cout << " tens: " << tens;
int ones = userNum % 10 / 1;
cout << " ones: " << ones << endl;
answers[0] = convert(thous, "M", "M", "M");
answers[1] = convert(hund, "C", "D", "M");
answers[2] = convert(tens, "X", "L", "C");
answers[3] = convert(ones, "I", "V", "X");
cout << answers[0] << endl << answers[1] << endl << answers[2];
cout << endl << answers[3] << endl;
} while (userNum >= 0);
system("PAUSE");
return 0;
}
string convert(int digit, string low, string mid, string high)
{
cout << digit << endl;
if (digit == 1)
{
return low;
}
if (digit == 2)
{
return low + low;
}
if (digit == 3)
{
return low + low + low;
}
if (digit == 4)
{
return low + mid;
}
if (digit == 5)
{
return mid;
}
if (digit == 6)
{
return mid + low;
}
if (digit == 7)
{
return mid + low + low;
}
if (digit == 8)
{
return mid + low + low + low;
}
if (digit == 9)
{
return low + high;
}
if (digit == 0)
{
return "";
}
}
But I would like to also provide an alternative implementation of the string conversion ( from http://rosettacode.org/wiki/Roman_numerals/Encode#C.2B.2B ):
std::string to_roman(unsigned int value)
{
struct romandata_t { unsigned int value; char const* numeral; };
const struct romandata_t romandata[] =
{
{1000, "M"}, {900, "CM"},
{500, "D"}, {400, "CD"},
{100, "C"}, { 90, "XC"},
{ 50, "L"}, { 40, "XL"},
{ 10, "X"}, { 9, "IX"},
{ 5, "V"}, { 4, "IV"},
{ 1, "I"},
{ 0, NULL} // end marker
};
std::string result;
for (const romandata_t* current = romandata; current->value > 0; ++current)
{
while (value >= current->value)
{
result += current->numeral;
value -= current->value;
}
}
return result;
}

Answer 4

I would suggest you this C++14 code:
#include <utility>
#include <string>
auto toRoman(unsigned arabic)
{
constexpr auto table = {
std::make_pair(1000u, "M"),
std::make_pair(900u, "CM"),
std::make_pair(500u, "D"),
std::make_pair(400u, "CD"),
std::make_pair(100u, "C"),
std::make_pair(90u, "XC"),
std::make_pair(50u, "L"),
std::make_pair(40u, "XL"),
std::make_pair(10u, "X"),
std::make_pair(9u, "IX"),
std::make_pair(5u, "V"),
std::make_pair(4u, "IV"),
std::make_pair(1u, "I")
};
std::string roman;
for (auto& pair: table)
{
while (pair.first <= arabic)
{
arabic -= pair.first;
roman += pair.second;
}
}
return roman;
}