【LeetCode】8. String to Integer (atoi)

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.

题意：把符合条件的字符串变为数字

难点：这个题不难，难在要考虑转换条件

　　1.连续的数字字符

　　2.连续的数字字符前面不能用‘+‘，’-’，之外的字符，而且加减号要和数字相接

　　3.连续的数字字符后面可以有字幕（不知道为什么这个可以）

　　4.考虑溢出

int myAtoi(char* str) {
    int len,i;
    len=strlen(str);
    long tmp=0;
    int flag=0;
    for(i=0;i<len;i++)
    {
        while(str[i]==' ')
            i++;
            if(str[i]=='+')
                {
                    flag=1;
                    i++;
                }
                else if(str[i]=='-')
                    {
                        flag=-1;
                        i++;
                    }
            if(flag&&!(str[i]<='9'&&str[i]>='0'))
                return 0;
        while(i<len&&(str[i]<='9'&&str[i]>='0'))
            {
                if(tmp<0)
                    tmp=tmp*10-(str[i]-'0');
                else
                    tmp=tmp*10+(str[i]-'0');
                if(-1==flag)
                    {
                        tmp*=-1;
                        if(tmp<0)
                             flag=1;
                    }
                if(tmp>INT_MAX)
                        return 2147483647;
                    else if(tmp<INT_MIN)
                        return -2147483648;
                i++;
            }
        while(i<len)
             i++;
    }
        return tmp;
}