CODEWITHSUNDEEP
javapi
Hannes
Hannes

Reputation: 27

How to change the sign ("+" "-") every other time in Java

I have to wright a function for Newtons approximation of Pi.

Newton calculated that Pi/(2* sqrt(2)) = 1+ 1/3 - 1/5 - 1/7 + 1/9 + 1/11 -...

public class newtonPi {

public static void main(String []args) {
    
    int n = 10;
    double piN = 0;
    int sign = -1;
    for(int i = 1; i < n; i+=2) {
        System.out.println("i:"+i+" sign:"+sign);
        piN += sign*(1.0/i);
        sign *= -1;
    }
    

System.out.println(piN*(2*Math.sqrt(2)));

}}

But with this approach, the sign changes everytime and not every other.

Thanks for the help :)

Upvotes: 0

Views: 397

Answers (2)

Bohemian
Bohemian

Reputation: 425198

The pattern repeats every 8. Use the remainder operator % (aka modulo):

sign = n % 8 > 4 ? -1 : 1;

Upvotes: 4

Heitor Paceli
Heitor Paceli

Reputation: 530

If I understood your question, you want to change the sign every two iterations, right? The problem is you're doing sign *= -1 on each iteration.

Try to use another variable in order to figure out if the sign must be inverted in the current iteration. Here is your code updated:

int sign = 1; // Start with positive
for(int i = 1,iteration = 0; i < n; i += 2,iteration++) {
  System.out.println("i:" + i + " sign:" + sign);
  piN += sign * (1.0 / i);
  if(iteration % 2 != 0){
    sign *= -1; // Change every 2 iterations, the odd ones
  }
}

Upvotes: 3

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