ya i am able to break the sentence into words. i am also able to get the size of each word but i am unable to write the code for printing the longest word. if u want then i can give u the code how to break the sentence into each single word.
At a glance, the logic looks okay. There are some nasty habits that should be eliminated though:
The conio library is not needed in this program, it and all functions from it should be removed to maximize portability. This header is not standard, so you're basically limiting yourself to Turbo C variants.
This is not standard either. If the compiler supports it, you're fine. If the compiler doesn't support it, you've invoked undefined behavior. Given the risk, it's much better to simply use int main() and return 0 at the end.
Please forget that gets exists. In the latest standard it's been deprecated, and there's no way to make it safe. If you try to input a string with more than 99 characters, you're basically screwed. fgets is the recommended alternative.
I won't go into a rant about clrscr and getch, because they're both functions from the conio library and I've already recommended that they be removed. However, if you want, I can go into more detail about why they're bad in this case.
One problem with the logic is that it doesn't take punctuation into account. Let's say your sentence is "Hi fellow pickles, I'm a pickle too!!!!!!". You'd incorrectly say that "too!!!!!!" is the longest word, because bangs aren't excluded from the count.