Fibonacci calculation

问题:

This program is supposed to get a Fibonacci number from the user and the program will calculate what it is while making sure that the user entered a positive number and a number no less than the Fibonacci number 70. So, if the user entered 7, it should print 13. The method fibcalc() is supposed to do the calculations. When I try and compile the program, I get the errors "method fibcalc in class Fibonacci cannot be applied to given types: System.out.printf("Fibonacci #%d is %f", num, fibcalc(num, x3)); and "cannot find symbol" return x3;Here's my code:

import java.util.Scanner;

public class Fibonacci
{
    public static void main ( String args[] ) 
    {
    Scanner input = new Scanner ( System.in );

        int num; 
        double x3 = 0;


           System.out.print("Which Fibonacci number would you like? ");
       num = input.nextInt(); 
           do
       {
        System.out.print("Which Fibonacci number would you like? ");
        num = input.nextInt(); 
    }while(num >= 0 && num <= 70);

    System.out.printf("Fibonacci #%d is %f", num, fibcalc(num, x3));

}


public static double fibcalc(int num) 
{
    int x1 = 0;
    int x2 = 1;

        if (num == 0)

            return 0;

        else if (num == 1)

            return 1;

        else

            for (int x3 = 0; x3 < num; x3++)
                {
                    x3 = x1 + x2;
                    x1 = x2;
                    x2 = x3;
                }
                return x3;

}
  }

There are probably other problems I've missed. I'm pretty new to java. Thanks in advance.

回答1:

The fibcalc() method has a single int parameter, but you are calling it with two parameters.

Change the call from

fibcalc(num, x3)

to

fibcalc(num)

ie change that line to:

System.out.printf("Fibonacci #%d is %f", num, fibcalc(num));

---

Also, if you want accurate numbers for your results, change from using double to using BigInteger, which can handle arbitrarily large numbers accurately.

回答2:

If you want to compute Fibonacci numbers, you can use direct (non-recursive, non-iterative) formula for Fibonacci numbers:

Fib(n) = (pow((1+sqrt(5))/2, n) + pow((1-sqrt(5))/2, n)) / sqrt(5)

It turns out that for all n >= 0, you can simplify this formula to:

Fib(n) = round(pow((1+sqrt(5))/2, n) / sqrt(5))

Knowing this, you can use following simple implementation for fibcalc:

public static double fibcalc(int num) {
    return Math.floor(Math.pow((1+Math.sqrt(5))/2, num) / Math.sqrt(5) + 0.5);
}

回答3:

You can also use the following calculator to calculate the Fibonacci sequence (using Javascript): enter link description here