LeedCode String to Integer (atoi)

网址：https://leetcode.com/problems/string-to-integer-atoi/description/

题目：

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

翻译：

 实现atoi方法（字符串转为整数）

思路：

解题思路：
题目简单，重要的是注意一些边界条件，如判定越界，是否含有非法字符，前空格去掉等

代码：

class Solution {public:   int myAtoi(string str) {          int index=0;          while(str[index]==' ')index++;          int flag=1;          if(str[index]=='-'){              index++;              flag=-1;          }else if(str[index]=='+'){              index++;          }          int res=0;          while(index<str.size()){              if(str[index]<'0' || str[index]>'9'){                  return flag*res;              }              int digit=str[index]-'0';              if(flag==1 && res*10.0+digit>INT_MAX){                  return INT_MAX;              }else if(flag==-1 && -(res*10.0+digit)<INT_MIN){                  return INT_MIN;              }              res = res*10+digit;              index++;          }          return flag*res;      }  };