How to Take input from user in c

In this video i have taught how to take input from user and then add,multiply,divide,subtract from it,Also there are other tricks you can learn from to master c like how to use endl to change line in the out what will happen if we don't do this,also the advantage of clrscr other wise it can ruin your output and how the output looks like if clrscr is not used and what will happen if we use it