字符串转换成整数

 

 

class Solution {
public:
    int invalid = 1;
    int StrToInt(string str) {
        
        bool minus = false;
        int index = 0;
        long long num = 0;
        if(str.size() != 0 && str[index] != '\0'){
            if(str[index] == '+')
                index++;
            else if(str[index] == '-'){
                minus = true;
                index++;
            }
            if(str[index] != '\0'){
                num = StrtoInt_Core(str,minus,index);
            }
        }
        return int(num);
    }
    long long StrtoInt_Core(string str,bool minus,int index){
        int length = str.size();
        long long num = 0;
        int flag = minus ? -1 : 1;
        for(;index < length;index++){
            if(str[index] >= '0' && str[index] <= '9'){
                num = num * 10 + flag * (str[index] - '0');
                int xxx = 0x80000000;
                if(num < xxx || num > 0x7FFFFFFF){
                    num = 0;
                    break;
                }
            }
            else{
                num = 0;
                break;
            }
        }
        if(str[index] == '\0')
            invalid = 0;
        return num;
    }
};