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]!=‘\0‘){
            i++;
        }
        if(str[i]==‘-‘&&str[i]!=‘\0‘){
            flag=0;
            i++;
        }else if(str[i]==‘+‘&&str[i]!=‘\0‘){
            i++;
        }
        for(;str[i]!=‘\0‘;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;
        
        
    }
};