Algorithm: Dog and chick

dog_and_chick.cpp

//============================================================================
// Name        : DogAndChick.cpp
// Author      : magicsih
// Version     :
// Copyright   : 
// Description : How many dogs and chicks in C++, Ansi-style
//============================================================================

#include <iostream>
#include <fstream>

using namespace std;

int main() {
	std::ifstream fin;
	fin.open("input.txt");
	int sumOfAnimals, sumOfLegs;
	char buf[5];

	string result;

	while(fin >> sumOfAnimals >> sumOfLegs) {
		if(sumOfAnimals == 0 && sumOfLegs == 0) {
			break;
		}

		if(sumOfAnimals > 1000 || sumOfLegs > 4000) {
			result.append("INPUT ERROR!\n");
			continue;
		}

		int dogs = (sumOfLegs - 2 * sumOfAnimals) / 2;
		int cheeks = sumOfAnimals - dogs;

		if(dogs < 0 || cheeks < 0) {
			result.append("0\n");
			continue;
		}

		_itoa_s(dogs, buf, 10);
		result.append(buf);
		result.append(" ");

		_itoa_s(cheeks, buf, 10);
		result.append(buf);
		result.append("\n");
	}
	fin.close();

	std::ofstream fout;
	fout.open("output.txt");
	fout << result.c_str();
	fout.close();

	return 0;
}

input

25 80
15 10
1500 2000
0 0