What is the most efficient way to calculate PI in C? : <p>I'm have to write a C program, what it does is takes a integer as input. And gives output to the input(th) number of PI after decimal. Like if input is 100, output will be 9(100th digit of pi, after decimal is 9). 
What will be the best algorithm for that?</p>

<p>p.s I don't want to save the value of pi into the string, and do it.</p>
