LeetCode String To Integer

Consider very carefully to cover all the possible input conditions!

atoi: string -> integer

input: str

1. size:

　　different C++ data type's size in different machine [list]: http://hi.baidu.com/yangyangye2008/item/ba0a35395420d2f9df222157

　　(default: int - 4 bytes)

2. begin (' ','+','-') , others' error

3. inside('0'-'9', ' '), others' error

4. attention to the return type: int

　　but set the string-num type "long long" first, then judge it.

　* if string-num's size is bigger than the int-type size, then return the biggest int(positive/negtive):

　　if(negtive)
　　{
　　　　ret = ret<=0x80000000 ? ~(unsigned int)ret+1 : 0x80000000;
　　}
　　else
　　{
　　　　ret = ret<=0x7FFFFFFF ? ret : 0x7FFFFFFF;
　　}

5. integer:     aN = ((((a1*10+a2)*10+...)*10...)+an-1)*10+an;

attach code:

class Solution {
public:
    int atoi(const char *str) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        
        long long ret = 0;
        int i = 0;
        bool negtive = false;
        
        while(str[i] == ' ') i++;
        
        if(str[i]=='+') i++;
        else if(str[i]=='-') {negtive=true;i++;}
        
        while(str[i]!='\0' && str[i]>='0' && str[i]<='9')
        {
            int d = str[i]-'0';
            ret = 10*ret+d;
            i++;
        }
        
        if(negtive)
        {
            ret = ret<=0x80000000 ? ~(unsigned int)ret+1 : 0x80000000;        
         }
         else
         {
            ret = ret<=0x7FFFFFFF ? ret : 0x7FFFFFFF;
         }
        
        return ret;
        
    }
};