Fibonacci java program

Question

Created a program that would input a number and provides its equivalent fibonacci number as an output. But there's something wrong with my code :c

import java.util.Scanner;
public class Fibonacci {
    public static void main(String[] args) {
        Scanner in = new Scanner (System.in);
        int prev, next, num, sum = 0, n;
        prev=next=1;

        System.out.print("Input number: ");
        num = in.nextInt();

        if ((num == 1) || (num ==2))
            System.out.println(prev);

        else {
            for( n=1; n<=prev; n++ ) {
                sum = prev + next;
                prev = next;
                next = sum;
            }

            System.out.println(sum);
        }

    }
}

Something's wrong I just can't see. Help? :c

Time to learn how to use a `debugger`. Better to learn how to debug now before you start writing longer and more complex programs. — Tdorno, Feb 21 '14 at 19:48
You might want to move this code into a method as well. Not sure if you've been exposed to recursion yet, but that's the best (read: most concise) way to solve this problem. — turbo, Feb 21 '14 at 19:53
Just to mention, as well as the [closed formula](http://en.wikipedia.org/wiki/Fibonacci_number#Closed-form_expression) `O(1)` version (subject to precision problems for large numbers, will require `BigDecimals` with a lot of decimal places for those), there are variations of the algorithm which costs `O(log(n))`[(java example)](http://stackoverflow.com/a/15093963/664577). — Anthony Accioly, Feb 21 '14 at 20:10

score 2 · Answer 1 · answered Feb 21 '14 at 19:45

2

You're stopping the loop when n reaches beyond prev, so you aren't getting the correct number. Stop it when you've passed num instead:

for(n = 1; n <= num; n++) {

Example run:

Input number: 6
21

answered Feb 21 '14 at 19:45

rgettman

176,041
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score 1 · Accepted Answer · answered Feb 21 '14 at 19:49

1

Change your for loop to this:

for( n=2; n<num; n++ )

That'll solve your problem.

Explanation: Since you've already determined that 1 or 2 will give you a 1, start your loop @ 2. Loop through until n becomes larger than the entered number. This will solve the problem you were having.

answered Feb 21 '14 at 19:49

Opzoleet

38
1
8

yeah, I have. I only went up to 10 places though. Or am I misunderstanding the problem posted? I understood the problem to say: 1 is 1, 2 is 1, 3 is 2, 4 is 3, 5 is 8, 7 is 13, etc... – Opzoleet Feb 21 '14 at 19:52
Thank you! :) It worked btw 5 is 5 though. Not 8 :) – Khelshy Mawnik Feb 21 '14 at 19:55
No problem, sometimes step away from the problem for a bit and draw it out to see what it should look like. Edit: Yeah, sry, didn't mean 5 is 8... type (5 is 5) – Opzoleet Feb 21 '14 at 19:57
i guess it's a typo cause there's no 6 :) – Khelshy Mawnik Feb 21 '14 at 19:57
ZouZou - I think the problem here was Khelshy was looking for the say 5th number in the Fib sequence, which would be 5, the 6th number would be 8, etc – Opzoleet Feb 21 '14 at 20:00
@Opzoleet Yes sorry! I misread this :) (actually the 5th number of the fib sequence is 3) – Alexis C. Feb 21 '14 at 20:05
How did it became 3 ._. I'm pretty sure it's 5. – Khelshy Mawnik Feb 21 '14 at 20:14

score 0 · Answer 3 · answered Feb 21 '14 at 19:45

0

If you want to get the fiboniki number times the user has given input then you need to iterate in for loop.

 for( n=1; n<=num; n++ ) {
                    sum = prev + next;
                    prev = next;
                    next = sum;
                    System.out.println(sum);
                }

Also to print the number you need to put it in the loop.

answered Feb 21 '14 at 19:45

Kick

4,823
3
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3

Instead of doing homework for people, why not explain the process of working through the problem and debugging code? – Kevin Workman Feb 21 '14 at 19:46
kk sir @KevinWorkman.It will be better if you wait for some time before downvote the answer – Kick Feb 21 '14 at 19:50

Fibonacci java program

3 Answers3