# Fibonacci series using java

I wrote this code to calculate Fibonacci numbers by specifying the size. The results are correct, however the one thing that concerns me is the negative sign for some numbers in the larger range of size input.
here is the code

``````import java.util.Scanner;

public class FibonacciSeries {

public static void main(String[] args) {
// TODO Auto-generated method stub
int a, c = 0;
int result = 0;
int b = 1;

Scanner scan = new Scanner(System.in);
System.out.println("Enter the Number to display Fibonacci Series");
a = scan.nextInt();

System.out.println("Fibonacci Seriers is as follows");

for (int i = 1; i <= a; i++) {
System.out.print(" "+result+" ");
result = c + b;
b = c;
c = result;

}

}

}
``````

As previously said, this function calculates fibonacci numbers by selecting the size. I read the article about it here according to that findings are right however the one thing that bothers me is the negative sign for some values in the greater range of size input.

1- I couldn’t identify a mistake in the code; how can I remove the negative values from the output?
2- Why are there positive values following certain negative values? 3- The first negative value is -1323752223, followed by a positive number.

Thank you very much.

1 Like

Corresponding tweet for this thread:

Share link for this tweet.

1 Like

The problem you are having is integer overflow. The int allocates enough memory to hold a number within a range (specifically 32 bits giving a range of 2^-31 through 2^31 which is -2147483648 to 2147483647), when you add two numbers together and the result is larger then this than it overflows the memory available. Due to the way in which numbers are represented and added in binary, the effect it has is that it wraps around so 2147483647 + 1 = -2147483648.

You can look into integer overflows, to fully understand what is happening it is best to look at how numbers are represented in binary, twos complement, and how to do addition/subtraction. However for the problem at hand you have two options.

First you can use a long which allocates twice as much memory for the numbers and will give you a much larger range before you run into the same problem, but you will run into the same problem with big enough numbers. This is the easiest option, you should be able to just change “int” to “long” when declaring the variables and you will be good.

Alternatively you can look at something like the BigInteger class which will be able to allocate the right amount of memory to hold larger numbers as required, with some small costs in performance and being more awkward to use in some situations.

2 Likes