#include <iostream>

using namespace std;

bool isValidInBase(string number, int base);
string addNumbersInBase(string num1, string num2, int base);
string subtractNumbersInBase(string num1, string num2, int base);
void getInputsForBase(string &num1, string &num2, int base);

int main (int argc, char * const argv[]) {
	int base;
	string number1, number2;
	int command = 0;
	
	cout << "\n\nNew Horizons Governors School Team B\n";
	cout << "Enter a base (0 < base < 10): ";
	cin >> base;
	
	while (base <= 0 || base > 10) {
		cout << "Invalid base; enter a new one\n";
		cout << "Enter a base (0 < base < 10): ";
		cin >> base;
	}
	
	do {
		cout << "Enter the number representing your command:\n";
		cout << "1. Add two base " << base << " numbers\n";
		cout << "2. Subtract two base " << base << " numbers\n";
		cout << "3. Exit\n";
		cout << "> ";
		cin >> command;
		
		if (command == 1) {
			getInputsForBase(number1, number2, base);
			cout << "The sum of " << number1 << " and " << number2 << " is " << addNumbersInBase(number1, number2, base);
			cout << " in base " << base << endl;
		}
		
		else if (command == 2) {
			getInputsForBase(number1, number2, base);
			cout << "The difference of " << number1 << " and " << number2 << " is " << subtractNumbersInBase(number1, number2, base);
			cout << " in base " << base << endl;
		}
		
		else if (command == 3);
		else cout << "Invalid command\n";
		
	} while (command != 3);
	
    return 0;
}

bool isValidInBase(string number, int base) {
	for (int i = 0; i < number.length(); i++)
		if (number[i] < '0' || number[i] > base + '0' - 1)
			return false;
	return true;
}


string addNumbersInBase(string num1, string num2, int base) {
	int n1Length = num1.length(), n2Length = num2.length();
	int n1, n2;
	int resultLength = (n1Length > n2Length ? n1Length : n2Length) + 1;
	int result, resultArray[resultLength];
	
	n1 = atoi(num1.c_str());
	n2 = atoi(num2.c_str());
	result = n1 + n2;
	
	int i;
	for (i = resultLength - 1; i >= 0; i--) {
		resultArray[i] = result % 10;
		result /= 10;
	}
	
	for (i = resultLength - 1; i > 0; i--) {
		while (resultArray[i] > base - 1) {
			resultArray[i] -= base;
			resultArray[i - 1]++;
		}
	}
	
	string stringResult = "";
	
	for (int i = 0; i < resultLength; i++)
		stringResult += resultArray[i] + '0';
	
	return stringResult;
}

string subtractNumbersInBase(string num1, string num2, int base) {
	int n1Length = num1.length(), n2Length = num2.length();
	int n1 = atoi(num1.c_str()), n2 = atoi(num2.c_str());
	int resultLength = (n1Length > n2Length ? n1Length : n2Length);
	int resultArray[resultLength];
	int n1Array[n1Length], n2Array[n2Length];
	bool negative = n1 < n2;
	
	//need to swap them
	if (negative) {
		int temp = n1;
		n1 = n2;
		n2 = temp;
		temp = n1Length;
		n1Length = n2Length;
		n2Length = temp;
	}
	
	for (int i = 0; i < resultLength; i++) {
		resultArray[i] = 0;
	}
	
	
	for (int i = resultLength - 1; i >= 0; i--) {
		if (resultLength - i > n1Length)
			n1Array[i] = 0;
		else
			n1Array[i] = num1[i] - '0';
		
		if (resultLength - i > n2Length)
			n2Array[i] = 0;
		else
			n2Array[i] = num2[i] - '0';
	}
	
	for (int i = resultLength - 1; i >= 0; i--) {
		if (n1Array[i] - n2Array[i] < 0) {
			n1Array[i - 1]--;
			n1Array[i] += base;
		}
		resultArray[i] = n1Array[i] - n2Array[i];
	}
	
	string stringResult = "";
	
	for (int i = 0; i < resultLength; i++)
		stringResult += resultArray[i] + '0';
	
	if (negative)
		stringResult.insert(0, "-");
	
	return stringResult;
}

void getInputsForBase(string &num1, string &num2, int base) {
	cout << "Enter the first number: ";
	cin >> num1;
	while (!isValidInBase(num1, base)) {
		cout << "Not valid, try again: ";
		cin >> num1;
	}
	
	cout << "Enter the second number: ";
	cin >> num2;
	while (!isValidInBase(num2, base)) {
		cout << "Not valid, try again: ";
		cin >> num2;
	}
}