LeetCode Length of Last Word

int lengthOfLastWord(const char *s) {
const char *lastspace = s;
if(!*s)
return 0;
while(*lastspace)
lastspace++;
int sum = 0;
lastspace--;
while(lastspace!=s&&*lastspace==' ')
lastspace--;
while(lastspace!=s&&*lastspace!=' ')
{
sum++;
lastspace--;
}
if(lastspace==s&&*lastspace!=' ')
sum++;
return sum;
}