String to Integer (atoi)

Class Solution {public:    int atoi (string str) {        long long result=0;        int flag=1;        int i=0;        while (str[i]== ' &&str[i]!= ') {            i++;        }        if (str[i]== '-' &&str[i]!= ') {            flag=0;            i++;        } else if (str[i]== ' + ' &&str[i]!= ') {            i++;        }        for (; str[i]!= '; i++) {            if (str[i]>= ' 0 ' &&str[i]<= ' 9 ') {                                                if (flag) {                    result=result*10+ str[i]-' 0 ';                    if (RESULT>0X7FFFFFFF)                    return 0x7FFFFFFF;                } else{                    result=result*10-(str[i]-' 0 ');                    if (result< (signed int) 0x80000000)                    return 0x80000000;                }             } else break;        }        return (int) result;}                    ;

Attention:

1, the space before the character processing;

2. Invalid character input

3, Integer cross-border problem, here used a small trick, the return type is defined as long long. Then separate to determine whether the cross

32-bit integer range ((signed int) 0x80000000~0x7fffffff)

String to Integer (atoi)