#include "stdafx.h"
#include <iostream>

double _atof_(const char *x);
double _pow_(int x, int y);

int main()
{
	printf("%lf\n", _atof_("3.141592"));
	printf("%lf\n", _atof_("-3.14159"));
	printf("%lf\n", _atof_("78"));
	printf("%lf\n", _atof_("-78"));
	printf("%lf\n", _atof_("3.14159_"));
	printf("%lf\n", _atof_("3.141.59"));
	printf("%lf\n", _atof_("-3."));
	printf("%lf\n", _atof_("-"));
	printf("%lf\n", _atof_("-b"));
	printf("%lf\n", _atof_("ABCDEFG"));

	std::cin.get();
    return 0;
}

double _atof_(const char *x)
{
	double res = 0.0;
	double res2 = 0.0;
	bool neg = false;
	int help = -1;
	int dot = 0;

	if (x[0] == '-')
	{
		neg = true;
	}
		
	for (int i = 0 + neg; x[i] != '\0'; i++)
	{
		int val = (x[i] - 48);

		if ((val < 0) || (val > 9))
		{
			if (val == -2 && i != 0 && dot == 0 && x[i+1] != '\0')
			{
				dot = i;
			}
			else
				return 0.0;
		}
		else if (dot == 0)
		{
			res += val / _pow_(10, i);
			help += 1;
		}
		else
		{
			res2 += val / _pow_(10, i-dot);
		}				
	}

	res *= _pow_(10, help + neg);
	res += res2;

	if (neg == true)
	{
		res -= res * 2;
	}
	return res;
}

double _pow_(int x, int y)
{
	if (y == 0)
		return 1;
	else if (y == 1)
		return x;
	else
	{
		int res = x;
		for (int i = 1; i < y; i++)
		{
			res *= x;
		}
		return res;
	}
	return 0.0;
}