Leetcode: atoi

class Solution {public:    int atoi(const char *str) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(str==NULL)            return 0;        int i=0;        bool negative=false;                //deal with spaces at the beginning of the string        while(str[i]==' ')            ++i;        //check if the number is negative        if(str[i]=='-'){            negative=true;            ++i;        } else if(str[i]=='+')                ++i;        //do the real thing        double result=0;        while(str[i]!='\0'&&str[i]>='0'&&str[i]<='9'){            int n=str[i]-'0';            result=result*10+n;            ++i;        }                //perform dound check        int output;        if(negative)            output=result>INT_MAX?INT_MIN:(~(unsigned int)result+1);        else output=result>=INT_MAX?INT_MAX:result;                return output;                    }};