Give in= to surrender to something. Give up= quite the opposite, for instance when you "quit" smoking you "give up" smoking. I give in to smoking = I submit myself to the habit, I can't "give up" smoking. I give up smoking = I quit smoking, I will not "give in" to smoking.

give in means To hand in; submit: the reporter gave in his report about the accident. give up means to surrender or stop doing something the thieves at last gave themselves up. my grandfather gave up smoking two years ago.

give up = no longer try give in = when you submit to an idea that is not your own