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BigInteger addition is always 0

I have the following problem, when I try to add to the BigIntegers sum, the result 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.

This is what happens on the terminal:

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

+3


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2 answers


It has to do with BigInteger

being immutable, which means its value doesn't change. Thus, it first.add(x)

will create a new one BigInteger

containing the result of calculations, i.e. First will reassign the result, eg first = first.add(...)

.



+11


source


The add

class method BigInteger

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

first += value;


in fact, you should do it like this:

first = first.add(value);
+1


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