leetcode-String to Integer (atoi)

class Solution {
public:
int atoi(const char *str)
{
bool negative = false;
while(*str==' ')str++   ;
if(*str=='-')
{
negative = true;
str++;
}
else if(*str=='+')
str++;
long long  result = 0;
while(*str!='\0')
{
if(*str>='0'&&*str<='9')
{
result = result * 10 + *str - '0';
str++;
}
else
break;
}

result =  negative?-result:result;
if(result>INT_MAX)
return INT_MAX;
else if(result<INT_MIN)
return INT_MIN;
return result;
}
};