How to calculate the sum of geometric series

Question

I want to calculate the sum of a geometric series. ie: 1 , 5 , 25 , 125 , etc I try to use the math formula to calculate it: a(r^n -1)/(r-1)

My code:

int a = 1;
int r = 5;
int deno = r -1;
int n = 3
int rn = r^n -1 ;

int total = a * rn / deno;

Apparently there is wrong with the code and only some values like the example I give works. I do not know why QAQ

I think the problem is the symbol ^ can anyone explain what ^ does in java? Appreciate it

show an example which doesn't work. Paste expected and evaluated result. — papaya, Feb 14 '20 at 07:03
Can you show the actual output of the code, and the desired output? — Sweeper, Feb 14 '20 at 07:03
In Java, you do not use `^` for power of numbers. It's actually the exclusive or operator. — dave, Feb 14 '20 at 07:07
@papaya the code I put on does not work. It is expected to print out 125, but it really prints out 6. I wonder why it resulted in this number? — smallnoob, Feb 14 '20 at 08:17

score 1 · Accepted Answer · answered Feb 14 '20 at 07:06

1

Atleast in Java 7, the symbol ^ does not mean power.

Try this, you would also like to put a condition where r>1 or r<1. Both have different formuals.

        int a = 1;
        int r = 5;
        int deno = r -1;
        int n = 3;
        double sum=a*(Math.pow(r, n)-1)/deno;

answered Feb 14 '20 at 07:06

so I need to use `Math.power(x, y)` instead of `^`. Ok got it. – smallnoob Feb 14 '20 at 08:14

1 Answers1