题目描述：
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.
这道题又涉及到整数处理，越界是必须要考虑的。一处理整数，我就想到栈，哎，代码写的太冗余了。贴下别人的吧
solution1：
int atoi(const char *str) { while (isspace(*str)) ++str; int sign = (*str == ‘-‘) ? -1 : 1; if(*str == ‘-‘ || *str == ‘+‘) ++str; long long res = 0; while (isdigit(*str)) { res = res * 10 + *str - ‘0‘; if (sign > 0 && res > INT_MAX) return INT_MAX; if(sign < 0 && -res < INT_MIN) return INT_MIN; ++str; } return res * sign; }
此法诀窍在于使用long long类型避免越界，如果不使用long long类型呢？
solution2：
int atoi(const char *str) { while (isspace(*str)) ++str; int sign = (*str == ‘-‘) ? -1 : 1; if(*str == ‘-‘ || *str == ‘+‘) ++str; int res = 0; while (isdigit(*str)) { int digit = *str - ‘0‘; if (res > (INT_MAX - digit)/10) return sign == 1 ? INT_MAX : INT_MIN; res = res * 10 + digit; ++str; } return res * sign; }
参考文章：http://blog.csdn.net/ithomer/article/details/8800530
类似文章：http://blog.csdn.net/linhuanmars/article/details/21145129
https://oj.leetcode.com/discuss/8886/my-simple-solution
PS：
另一个处理整数的算法题 Reverse Integer：http://www.cnblogs.com/gattaca/p/4177810.html
原文：http://www.cnblogs.com/gattaca/p/4190135.html