8. String to Integer (atoi)

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.

Update (2015-02-10):
The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button  to reset your code definition.

思路：

本题是字符串转整数，本题要注意的是字符串有正负之分，而且当数值溢出且为正数时，直接输出2147483647，当数值溢出且为负数时，直接输出-2147483648

代码：

class Solution {public:    int myAtoi(string str) {    long s = 0;      bool flag = false;      string::iterator itr=str.begin();      while(*itr==' ')      {          itr++;      }        if(*itr=='-'||*itr=='+')      {          if(*itr=='-')          flag=true;          itr++;      }        while(*itr>='0'&&*itr<='9')      {          s=s*10+*itr-'0';          itr++;          if(s>=2147483648&&flag==true)          {              // cout<<s<<endl;            s=2147483648;              break;          }        else if(s>=2147483647&&flag==false)          {              // cout<<s<<endl;            s=2147483647;              break;          }    }      return (int)s*(flag?-1:1);      }};