模拟C库中atoi与itoa

int my_atoi(char*str)
{
    if (str == NULL)
        return 0;
    bool flag = true;
    if (*str++ == '-')
        flag=false;
    int res = 0;
    while (*str >= '0'&&*str <= '9')
    {
        res = res*10+(*str - '0');
        str++;
    }
    if (flag == false)
        res = 0 - res;
    return res;
}


char* my_itoa(int num, char*str, int radix)//转为radix进制
{   /*索引表*/
    char index[] = "0123456789ABCDEF";
    unsigned unum;/*中间变量*/
    int i = 0, j, k;
    /*确定unum的值*/
    if (radix == 10 && num<0)/*十进制负数*/
    {
        unum = (unsigned)-num;
        str[i++] = '-';
    }
    else unum = (unsigned)num;/*其他情况*/
    /*转换*/
    do{
        str[i++] = index[unum % (unsigned)radix];
        unum /= radix;
    } while (unum);
    str[i] = '\0';
    /*逆序*/
    if (str[0] == '-')k = 1;/*十进制负数*/
    else k = 0;
    char temp;
    for (j = k; j <= (i - 1) / 2; j++)
    {
        temp = str[j];
        str[j] = str[i - 1 + k - j];
        str[i - 1 + k - j] = temp;
    }
    return str;
}