Übung atof Leange

#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;
}