49. Convert String to Integer

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;

enum Status {KValid = 0, KInvalid};
int g_nStatus = KValid;

long long StrToIntCore(const char* digit, bool minus)
{
    long long num = 0;

    while (*digit != '\0')
    {
        if (*digit >= '0' && *digit <= '9')
        {
            int flag = minus ? -1 : 1;
            num = num * 10 + flag * (*digit - '0');

            if ((!minus && num > 0x7FFFFFFF) || (minus && num < (signed int)0x80000000))
            {
                num = 0;
                break;
            }

            digit++;
        }

        else
        {
            num = 0;
            break;
        }
    }

    if (*digit == '\0')
    {
        g_nStatus = KValid;
    }

    return num;

}

int StrToInt(const char* str)
{
    g_nStatus = KInvalid;
    long long num = 0;

    if (str != NULL && *str != '\0')
    {
        bool minus = false;
        if (*str == '+')
        {
            str++;
        }
        else if (*str == '-')
        {
            str++;
            minus = true;
        }

        if (*str != '\0')
        {
            num = StrToIntCore(str, minus);
        }
    }

    return (int) num;

}



int main()
{
    int num = StrToInt("1234");
    cout << num << endl;

    return 0;
}