【leetcode】String to Integer (atoi)

class Solution {
public:
int atoi(const char *str) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
bool negative=false;
while(*str==' ')
str++;

if(*str=='-')
{
negative = true;
str++;
}
else if(*str=='+')
str++;

long long res=0;
while(*str!='\0')
{
if(*str>='0'&&*str<='9')
{
res=res*10+(*str-'0');
str++;
}
else
break;
}

if(negative==true)
res = res*(-1);

if(res>INT_MAX)
return INT_MAX;
else if(res<INT_MIN)
return INT_MIN;
else
return res;
}
};