#include "Function.h"
 
 
CFunction::~CFunction(void)
{
}
 
int CFunction::GetNextValue(int & i)
{
	string sBuffer;
	char szFormula[255];
	strcpy_s(szFormula, 255, _sFunc.c_str());
	bool numStream(false);
	for (i = i; i < strlen(szFormula); ++i)
    {
       if (isdigit(szFormula[i]))
       {
		   //add the digit to the buffer
            numStream = true;
			sBuffer += szFormula[i];
       }
	   if (numStream && (!isdigit(szFormula[i]) || i == strlen(szFormula) - 1))
	   {
		   return atoi(sBuffer.c_str()); //return the buffer, converted to int
	   }
	   if (szFormula[i] == '(')
	   {//solve what's inside brackets first!
		   if (numStream)
			   throw exception ("Bracket error");
		   string tmp(ToCloseBracket(i));
		   return CFunction(tmp).Solve();
	   }
	}
	//error flag
	return -1;
}
 
string CFunction::ToCloseBracket(int & iIndex)
{
//problem function!!!***********************
	string sBuffer = "";
	int iCount(0), iCount2(0);
	for (int i(iIndex); i < strlen(_sFunc.c_str()); ++i)
	{
		if (_sFunc[i] == '(')
			iCount++;
	}
	while (iCount2 < iCount)
	{
		if (_sFunc[iIndex++] == ')')
			iCount2++;
		else
			sBuffer += _sFunc[iIndex];
	}
	return sBuffer;
}
 
int CFunction::Solve(char var)
{
	int i(0),
		iTmpVal(0),
		iReturn(0);
	char op(0);
	iReturn = GetNextValue(i);
	while (i < strlen(_sFunc.c_str()) - 1)
	{
		op = GetNextOp(i);
		iTmpVal = GetNextValue(i);
		switch (op)
		{
		case '+': iReturn += iTmpVal; break;
		case '-': iReturn -= iTmpVal; break;
		default: break;
		}
	}
	return iReturn;
}
 
char CFunction::GetNextOp(int & i)
{
	for (i = i; i < strlen(_sFunc.c_str()); ++i)
       if (_sFunc[i] == '+' || _sFunc[i] == '-' || _sFunc[i] == '*' || _sFunc[i] == '/')
		   return _sFunc[i];
	//error flag
	return -1;
}

#pragma once
#pragma warning(disable: 4018)
#include <iostream>
#include <string.h>
using namespace std;
 
class CFunction
{
protected:
	string _sFunc;
	int    _iCursor;
	int GetNextValue(int &);
	char GetNextOp(int &);
	string ToCloseBracket(int &);
public:
	bool SetFunc(string);
	int Solve(char = 0);
	CFunction(string s): _iCursor(0)
	{
		_sFunc = s;
	}
	~CFunction(void);
};

#include <string>
#include <iostream>
using namespace std;
#include "Function.h"
 
int main()
{
	char szBuffer[255];
	string sBuffer = "";
	cout << "Enter formula: ";
	cin.getline(szBuffer, 254);
	sBuffer = szBuffer;
	CFunction myFunc(sBuffer);
	cout << sBuffer << " = " << myFunc.Solve() << endl;
	cin.get();
	return 0;
}