Number to Words

main.cpp

#include <iostream>
#include <ctime>
#include <string>

using namespace std;

string convert(unsigned long n) {
	static char *formats[16] = {
		"", "%s%s%s", "%s%s", "%s%s-%s",
		"%s hundred", "%s hundred and %s%s", "%s hundred and %s", "%s hundred and %s-%s",
		"", "%s%s%s %s", "%s%s%s %s", "%s%s-%s %s",
		"%s hundred %s%s%s", "%s hundred and %s%s %s", "%s hundred and %s%s %s", "%s hundred and %s-%s %s"
	};
	
	static char *ones[20] = {
		"", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine",
		"ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"
	};
	
	static char *tens[10] = {"", "", "twenty", "thirty", "fourty", "fifty", "sixty", "seventy", "eighty", "ninety"};
	static char *scales[8] = {"", "thousand", "million", "billion", "trillion", "quadrillion", "quitillion", "sextillion"};
	
	if (n == 0) return "zero";
	
	string sections;
	
	for (unsigned s = 0; s < 8 && n > 0; s++) {
		unsigned o = n % 10; n /= 10;
		unsigned t = n % 10; n /= 10;
		unsigned h = n % 10; n /= 10;
		
		if (t == 1) {
			o += 10; t = 0;
		}
		
		unsigned f = (s > 0) * 8 + (h > 0) * 4 + (t > 0) * 2 + (o > 0);
		char section[43]; // 5 + 13 + 7 + 1 + 5 + 1 + 11 = 43
		
		sprintf(section, formats[f], ones[h], tens[t], ones[o], scales[s]);
		
		if (sections.length() > 0) {
			sections.insert(0, ", ");
		}
		
		sections.insert(0, section);
	}
	
	return sections;
}

int main(int argc, const char *argv[]) {
	static unsigned long numbers[1000];
	static size_t count = 1000;
	static clock_t start, ticks;
	
	for (size_t g = 0; g < count; g++) {
		srandomdev(); numbers[g] = random(); // Yes, I know I shouldn't seed it every time...
	}
	
	start = clock();
	
	for (size_t i = 0; i < count; i++) {
		string converted = convert(numbers[i]);
		
		printf("%lu = %s\n", numbers[i], converted.c_str());
	}
	
	ticks = clock() - start; printf("\n%ld clock ticks (%ld avg/num)", ticks, ticks / count);
	
	return 0;
}