for(int i=0; num_to_parse; i++)

wut

Why is `num_to_parse` your condition? Then you have `if (i == num_to_parse)` in there, too? That's odd. I'd rewrite this as:

    for(int i=0; i <= num_to_parse; i++) {
      int point_end = num_to_parse - i - 1;
      if(inputString[i] == inputString[point_end]) {
        continue;
      } else {
        return false;
      }
    }
    return true;

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While I was writing that, I realized that your indentation is... odd, to say the least. Please don't use things like `}}` in code, ever, for any reason, and indent things consistently.

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[`using namespace std` is a bad idea](http://stackoverflow.com/q/1452721/1863564). Please don't do it.

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    printf("%s", is_palidrome(inputString)?"This is a palindrome.":"Not a palindrome.");

This is just... weird. I mean, first of all, you don't have a trailing newline, so it might never output anything at all. In my C IDE, for example, it would, but on my Bash console, it'd definitely look odd (`This is a palindrome.q@my-hostname ~>`), if it prints at all. Even ignoring that inconsistency... why do it like that? The ternary just makes it more complicated than it has to be.

If you insist on using C functions (more on that later), do this:

    if (is_palindrome(inputString)) {
      puts("This is a palindrome.");
    } else {
      puts("Not a palindrome.");
    }

The C++ equivalent should be fairly straightforward; replace the `puts(...)` with `std::cout << ... << "\n";`, or `std::endl` in place of `"\n"` if you want to be paranoid about flushing every single line instead of just ensuring that it's flushed in a few key places (which is what I do in performance-critical stuff, because writing to the console is _slow_, and until you tell them to, most C++ standard libraries will avoid doing it for as long as is reasonable)

---

Now to talk about that "using C functions" thing. Why are you doing it at all? You have _all of C++'s power_ to bring to bear, but you don't. If you want to write this in C, write it in C -- it'd only be changing, like four lines. Maybe less. Don't use just a tiny part of C++. 

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With regards to your original concern about speed, you're doing this in O(n) (as far as I can tell), which is the absolute lower limit, and you're hitting the low end of that (n/2) by only going halfway.