How to compute PI

[Liang Cao]

public class ComputePI {
	public static void main(String args[]){
		double sum = 0.0;
		int maxDemo = 10000000;
		
		for (int denom = 1; denom < maxDemo; denom= denom + 2 ){
			if (denom%4 == 1){
				sum += (double) (4/denom);
			} else if (denom%4 ==3){
				sum -= (double)(4/denom);
			} else {
				System.out.println("The system has gone crazy");
			}
		}
		System.out.println("PI is " + sum);
       }
}

My output is : PI is 3.0
The correct ans should be 3.141592653589793

Code tags added - SS

 

[Someone Somewhere]

I think you're having issues with integer rounding - it's dividing an integer by an integer, so won't do floating point math.

Try using 4.0 instead of 4.

 

[Alabalcho]

Just a note on the algorithm used: As you probably know, PI is irrational number, so any number of digits will be just a close value of PI, never full value, so there is no "correct" answer.

 

[Pinhedd]

I think you're having issues with integer rounding - it's dividing an integer by an integer, so won't do floating point math.

Try using 4.0 instead of 4.

This is correct. The typecast is applied after the division. Type denom as a float (this is fine since it's never a fraction so the equality won't fail) or type the literal as a float "4.0f"

 

[Alabalcho]

One more note about precision. Last term to be applied to above sum will be 4.0/9,999,999. This will affect seventh digit after the decimal point, and the result will have only six correct digits - far away from the target of 3.141592653589793