IntegerToWords.cpp

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

void makeMapping(map<int, string>& mapping) {
	mapping[0] = "";
	mapping[1] = "One";
	mapping[2] = "Two";
	mapping[3] = "Three";
	mapping[4] = "Four";
	mapping[5] = "Five";
	mapping[6] = "Six";
	mapping[7] = "Seven";
	mapping[8] = "Eight";
	mapping[9] = "Nine";
	mapping[10] = "Ten";
	mapping[11] = "Eleven";
	mapping[12] = "Twelve";
	mapping[13] = "Thirteen";
	mapping[14] = "Fourteen";
	mapping[15] = "Fifteen";
	mapping[16] = "Sixteen";
	mapping[17] = "Seventeen";
	mapping[18] = "Eighteen";
	mapping[19] = "Nineteen";


	mapping[20] = "Twenty";
	mapping[30] = "Thirty";
	mapping[40] = "Forty";
	mapping[50] = "Fifty";
	mapping[60] = "Sixty";
	mapping[70] = "Seventy";
	mapping[80] = "Eighty";
	mapping[90] = "Ninety";
}

string getTensWords(int num, map<int, string>& mapping) {
	if(num<=20) {
		return mapping[num];
	}

	int tens = (num/10) * 10;
	int ones = num%10;
	string ans = mapping[tens];
	if(ones > 0) {
		ans = ans + " " + mapping[ones];
	}
	return ans;
}


string getHunderedsWords(int num, map<int, string>& mapping) {
	//cout << num << ": ";
	int rem = num%100;
	num = num/100;
	string output = "";

	if(num > 0) {
		output = mapping[num];
		output = output + " " + "Hundered";
		if(rem > 0) {
			output += " ";
		}
		//cout << output << ", ";
	}

	if(rem>0) {
		string t = getTensWords(rem, mapping);
		//cout << t << endl;
		output = output + t;

	}
	return output;
}

string getBaseString(int base, int num, int rem) {
	if(base==0 || num==0) {
		return "";
	}

	switch(base) {
		case 1: return "Thousand";
		case 2: return "Million";
		case 3: return "Billion";
	}
}

string numberToWords(int num) {
	if(num == 0) {
		return "Zero";
	}

	map<int, string> mapping;
	makeMapping(mapping);
	int base = 1;
	string output = "";

	while(num>0) {
		int rem = num%1000;
		num = num/1000;

		string h = getHunderedsWords(rem, mapping);
		string baseString = getBaseString(base, num, rem);

		//cout << h << endl;
		if(h.length()>0) {
			if(output.length() == 0) {
				output = h;
			}
			else {
				output = h + " " + output;
			}
		}
		if(baseString.length()>0 && num%1000 > 0) {
			if(output.length()>0) {
				output =  " " + output;
			}
			output = baseString + output;
		}

		base++;
	}    
	return output;
}

int main() {
	int n = 1000000;
	string output = numberToWords(n);
	cout << n << endl;
	cout << output << endl;
	return 0;
}