Number at f(93) in fibonacci series has negative value, how?

Question

I am trying to printout fibonacci series upto \'N\' numbers. All works as per expectation till f(92) but when I am trying to get the value of f(93), values turns out in nega

Answer 1

This happened because the long type overflowed. In other words: the number calculated is too big to be represented as a long, and because of the two's complement representation used for integer types, after an overflow occurs the value becomes negative. To have a better idea of what's happening, look at this code:

System.out.println(Long.MAX_VALUE);
=> 9223372036854775807  // maximum long value
System.out.println(Long.MAX_VALUE + 1);
=> -9223372036854775808 // oops, the value overflowed!

The value of fibo(93) is 12200160415121876738, which clearly is greater than the maximum value that fits in a long.

This is the way integers work in a computer program, after all they're limited and can not be infinite. A possible solution would be to use BigInteger to implement the method (instead of long), it's a class for representing arbitrary-precision integers in Java.