#include <iostream>
#include <string>

using namespace std;

class PStack
{
public:

	PStack();

	void parse( char* expression );

	bool isoper( std::string str );
	bool isfloat( char* );
	void push( double val );
	void docalc( std::string oper );

	double gettop();

private:

	double Stk[100];
	double *It;
	int opers_num;
	const char** valid_opers;// = { "+", "-", "*", "/", "^" };

};

bool PStack::isfloat( char* str )
{
	char* ch = str;

	do 
	{
		
		if( *ch != '.' )
		{
			if( *ch > '9' || *ch < '0')
			{
				return false;
			}
		}

	} while ( *(++ch) );

	return true;
}

bool PStack::isoper( std::string str )
{
	for(int i = 0; i < 5; i++)
	{
		if( str == valid_opers[i] )
		{
			return true;
		}
	}

	return false;
}



void PStack::parse( char* expression )
{
	char* pch = strtok(expression, " ");

	do 
	{

		if( !isoper( pch ) )
		{
			if( isfloat( pch ) )
			{
				this->push(atof(pch));
			}
			else
			{
				printf( "ERROR TYPE\n" );

				return;
			}
		}
		else
		{
			this->docalc( pch );
		}

	} while (pch = strtok( NULL, " "));
}

PStack::PStack()
{
	It = Stk;
	opers_num = 5;
	valid_opers = (const char**)malloc( sizeof( char* ) * opers_num);

	valid_opers[0] = "+";
	valid_opers[1] = "-";
	valid_opers[2] = "*";
	valid_opers[3] = "/";
	valid_opers[4] = "^";
}

void PStack::push( double val )
{
	*It++ = val;
}

void PStack::docalc( std::string oper )
{
	if( It - 2 >= Stk)
	{
		double vals[2] = {*(It-2), *(It-1)};

		It -= 2;

		if( oper == "+" )
		{
			this->push( vals[0] + vals[1] );
		}
		else if (oper == "-")
		{
			this->push( vals[0] - vals[1] );
		}
		else if (oper == "*")
		{
			this->push( vals[0] * vals[1] );
		}
		else if (oper == "/")
		{
			this->push( vals[0] / vals[1] );
		}
		else if (oper == "^")
		{
			this->push( pow(vals[0], vals[1]) );
		}
	}
}

double PStack::gettop()
{
	return *( It - 1 );

	return 0;
}

int main()
{
	PStack ps;
	char ch[] = "1.0 2.0 1.0 + + 2.0 *";
	ps.parse(ch);

	printf("%f", ps.gettop());
	getchar();
}