Recursion... please help!

Question

How can I develope a code that understands the Fibonacci-system? Say the answer that's gonna show on the console is fab(10)=89...
All I know is is
fab(0) = 0
fab(1) = 1
fab(2) = 1 = 0+1
fab(3) = 2 = 1+1
fab(4) = 3 = 1+2 and so on...

Answer 1

Just out of curiousity since you said that recursion
is a bad way to get the Fibonacci numbers... Can we
for instance use loop instead? But how? Here's a recursive and an iterative version. When n is like 40 the recursive takes seconds while the iterative isn't even measurable. 40 iterations in a while-loop and a few additions/assignments is nothing. Never use recursion when there's an obvious iterative alternative,
public static long fib1(int n) { // recursive
   return n<=2 ? 1 : fib1(n-1) + fib1(n-2); 
public static long fib2(int n) { // iterative
   long prev=1;
   long fib=1;
   while (--n > 1) {
      long t = fib;
      fib = fib + prev;
      prev = t;
   return fib;
}