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

You've encountered an integer overflow:

 4660046610375530309 <-- term 91
+7540113804746346429 <-- term 92
====================
12200160415121876738 <-- term 93: the sum of the previous two terms
 9223372036854775808 <-- maximum value a long can store

To avoid this, use BigInteger, which can deal with an arbitrary number of digits.
Here's your implementation converted to use BigDecimal:

public String fibo(int x){
    BigInteger[] arr = new BigInteger[x+1];
    arr[0]=BigInteger.ZERO;
    arr[1]=BigInteger.ONE;
    for (int i=2; i<=x; i++){
        arr[i]=arr[i-2].add(arr[i-1]);
    }
    return arr[x].toString();u
}

Note that the return type must be String (or BigInteger) because even the modest value of 93 for x produces a result that is too great for any java primitive to represent.