CODEWITHSUNDEEP
javaadditionbigintegerfactorial
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Reputation: 4783

BigInteger addition always 0

I have the following issue: when trying to add to a sum of BigIntegers the outcome remains 0.

Here is the code:

 public void NumberOfOutcomes(int x, int y){
   BigInteger first = BigInteger.valueOf(0);
   BigInteger second = BigInteger.valueOf(0);
   for(int i = 0; i <= (x / 2); i++){
       first.add( fac(x - i).divide((fac(x - 2*i).multiply(fac(i)))) );
       System.out.println("First " + first.add( fac(x - i).divide((fac(x - 2*i).multiply(fac(i)))) ));
    }

   for(int i = 0; i <= (y / 2); i++){
       second.add( fac(y - i).divide((fac(y - 2*i).multiply(fac(i)))) );
       System.out.println("Second " + second.add( fac(y - i).divide((fac(y - 2*i).multiply(fac(i)))) ));
    } 
   System.out.println("First " + first);
   System.out.println("Second " + second);
   System.out.println(first.multiply(second));
   }

Here fac is the factorial function.

Here is what comes on the terminal:

points1.NumberOfOutcomes(2, 3)
First 1
First 1
Second 1
Second 2
First 0
Second 0
0

Upvotes: 8

Views: 6305

Answers (2)

Ahmad Hosny
Ahmad Hosny

Reputation: 597

The add method of BigInteger class returns the sum of the operand and the value already stored in the the object itself. But it does not store the result in the object (first or second). It doesn't work in the same way as 

first += value;

actually, you have to make it look like this:

first = first.add(value);

Upvotes: 1

Tedil
Tedil

Reputation: 1933

This is because BigInteger is immutable which means that its value does not change. So first.add(x) will create a new BigInteger containing the computations result, i.e. just reassign the result to first, like first = first.add(...).

Upvotes: 22

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