Leetcode008. String to Integer (atoi)

 /* improvement on dealing  with overflow accroding to this:
  * https://discuss.leetcode.com/topic/57452/c-solution-beats-100
  *
  * be careful about the INT_MAX and INT_MIN
  * this atoi is not thinking about special char like dot and so on.
  */

 class Solution {
 public:
     int myAtoi(string str) {
        int i,nega_sign=;
        long long int re=;  //long long re to avoid overflow
        for(i=;i<str.size();i++)       //skip to all the blank in the front of the string
        {
            if(str[i]!=' ')break;
        }
        if(str[i]=='+')i++;             // deal with signature
        else if(str[i]=='-'){ nega_sign=-;i++;}
        while(i<str.size()&&isdigit(str[i]))
 /*when the string is over or the current char is not a valid integral number,no more conversion will be performed.
 */
        {
                re=re*+str[i]-'';
                if(nega_sign==-&& -*re<=INT_MIN)return INT_MIN;      //overflow
                else if (nega_sign==&&re>=INT_MAX)return INT_MAX;
                i++;
        }
        return re*nega_sign;
     }
 };