#include <iostream>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>

std::string getNumber();
std::string getOperation();
void NumberCheck(std::string number);
void OperationCheck(std::string operation);
double Calculate(std::string FirstNumber, std::string Operation, std::string SecondNumber);
double Round(double result);
void ExitProgram();

const std::vector<char> OperationList = {'+', '-', '*', '/', '%', '^'};

int main()
{
	// Get Data
	std::string FirstNumber = getNumber();
	std::string Operation = getOperation();
	std::string SecondNumber = getNumber();

	// Error Check
	NumberCheck(FirstNumber);
	OperationCheck(Operation);
	NumberCheck(SecondNumber);

	// Calculate
	double result = Calculate(FirstNumber, Operation, SecondNumber);

	//Round
	result = Round(result);

	std::cout << "Result: " << result;
	return 0;
}

std::string getNumber()
{
	std::string number;

	std::cout << "Enter Number: ";
	std::getline(std::cin, number);

	return number;
}

std::string getOperation()
{
	std::string operation;

	std::cout << "Enter Operation: ";
	std::getline(std::cin, operation);

	return operation;
}

void NumberCheck(std::string number)
{
	if (!number.empty() && std::all_of(number.begin(), number.end(), ::isdigit))
	{
		return;
	}
	else
	{
		ExitProgram();
	}
}

void OperationCheck(std::string operation)
{
	for (int i = 0; i < OperationList.size(); i++)
	{
		if (OperationList[i] == operation[0])
		{
			return;
		}
		else if (i + 1 == OperationList.size())
		{
			exit(0);
		}
	}
}

double Calculate(std::string FirstNumber, std::string Operation, std::string SecondNumber)
{
	double result;

	char operation = Operation[0];
	double x = std::stoi(FirstNumber);
	double y = std::stoi(SecondNumber);

	if (operation == OperationList[0])
	{
		result = x + y;
	}
	else if (operation == OperationList[1])
	{
		result = x - y;
	}
	else if (operation == OperationList[2])
	{
		result = x * y;
	}
	else if (operation == OperationList[3])
	{
		result = x / y;
	}
	else if (operation == OperationList[4])
	{
		result = std::fmod(x, y);
	}
	else if (operation == OperationList[5])
	{
		result = pow(x, y);
	}

	return result;
}

double Round(double result)
{
	std::vector<int> roundTo = {51, 75, 20};
	std::vector<int> minMax;

	std::sort(roundTo.begin(), roundTo.end());

	if (result < roundTo[0])
	{
		return roundTo[0];
	}
	if (result > roundTo[roundTo.size() - 1])
	{
		return roundTo[roundTo.size() - 1];
	}

	for (int i = 0; i < roundTo.size() - 1; i++)
	{
		if (result > roundTo[i] && result < roundTo[i + 1])
		{
			minMax.push_back(roundTo[i]);
			minMax.push_back(roundTo[i + 1]);
		}
	}

	if ((minMax[1] - minMax[0]) / 2 + minMax[0] <= result)
	{
		return minMax[1];
	}
	else
	{
		return minMax[0];
	}

	return result;
}

void ExitProgram()
{
	std::string pause;
	system("CLS");
	std::cout << "Invalid Number";
	std::getline(std::cin, pause);
	exit(0);
}