Recursively compute the Nth Fibonacci number:

[aesoprock00]

so, i've got an assignment for a class that i need some help with. What i need to do is write a program that will compute a Fibonacci number using a recursive method.
i've got this:
/**
Class that recursively computes the nth Fibonacci number.
*/
public class Fib {

public static void main(String[] args) {
// Compute a few that are easy to check
for (int i = 0; i < 16; i++) {
System.out.println("F[" + i + "] = " + fib(i));
}

// Then compute some larger ones
for (int i = 2; i < 5; i++) {
System.out.println("F[" + (i * 10) + "] = " + fib(i * 10));
}
}

/**
Returns the nth Fibonacci number
*/
public static int fib(int n) {


// --------------------------------
// ----- ENTER YOUR CODE HERE -----
// --------------------------------


// --------------------------------
// --------- END USER CODE --------
// --------------------------------


}

}
but i'm somewhat confused by what i need to enter in the actual method itself. does anyone know anything about recursion or the Fibonacci numbers? i can probably explain a little better if anyone needs it. Thanks for checking this out and even more thanks to anyone who knows what to do/how to explain it to me!

Fibonacci numbers are F(0) is 1, F(1) is 1, F(2) is 2, F(3) is 3, F(4) is 5... and in general F(i+2)=[F(i) +F(i+1)]

Thanks again!

[nspils]

I think you would have a better time if you re-wrote your formula to be F(i) = F(i-1) + F(i-2). The progression goes fib(1) = 1, fib(2) = 1, fib(3) = 2, fib(4) = 3, fib(5) = 5, fib(6) = 8, etc....

Remember for a recursive function you need to have a "base case" or two ...
F(0) = 0;
F(1) = 1;
F(2) = 1;
You can then write the function as being
F(i) = F(i-1) + F(i-2) for all i >= 3.

So you can write your binary recursive function as:

fib(n)
if( n == 1 || n == 2 )
return 1;
else
return fib(n-1) + fib(n-2)

[aesoprock00]

Thanks nspils! i modified the program to:
public class Fib {

public static void main(String[] args) {
// Compute a few that are easy to check
for (int i = 0; i < 16; i++) {
System.out.println("F[" + i + "] = " + fib(i));
}

// Then compute some larger ones
for (int i = 2; i < 5; i++) {
System.out.println("F[" + (i * 10) + "] = " + fib(i * 10));
}
}

/**
Returns the nth Fibonacci number
*/
public static int fib(int n)
{

if( n == 0 || n == 1 )
return (1);
else
return fib(n-1) + fib(n-2);

}

}

and it works perfectly! Thanks for the help. i even understand it! but, where you've got if(n==1 || n==2) should actually be 0 and 1, because of the way the Fibonacci numbers work. Thanks a ton though!

What i want to do next is modify the program so that it asks the user to enter a number (possibly via bufferedReader or JOptionPane) and then give the Fibonacci number as a response to the users entered number. i'm still working on that!

[nspils]

You're welcome. Look again at your definitions within the Fib class. Fib(3) = 2, not 3; Fib(4) is 3, Fib(5) is 5 ... Check it out - look in your text book or run a "Google" search - the base cases are Fib(1) and Fib(2) are both 1, not Fib(0) and Fib(1) ... Since there is no definition for Fib(0), perhaps you should test to make sure that a positive integer is entered ...

A textfield, alone or inserted into some other container inserted into your GUI will be the window for inputting a value. You can use a string function to cast the value input to an int to be fed to your function, or you can use the Scanner class. There was a Java "Tech Tip" published on March 8, 2005 talking about the Scanner class as an input acceptance and evaluation tool. You can find it at:

http://java.sun.com/developer/JDCTec...05/tt0308.html

[infinityj]

How i see my java version from the cmd command

please tell me...........thanks