Thread: Need help with my standard deviation code.

Here is the data set that is given as an example:

1 2 3 4.5 5.6 6 7 8 9 10

They give the answer as: 2.99794

Here is my code:

import java.util.*;
public class Exercise05_21 {
    public static void main(String [] args){
        Scanner s = new Scanner(System.in);
 
        System.out.print("Enter ten numbers: ");
 
            double[]x = new double[10];
 
            int i;
 
            for(i = 0;i < 10; i++){
 
                x[i] = s.nextDouble();
            }
 
 
            double mean = mean(x, i);
 
            double deviation = var(x);
 
            System.out.println("The mean is " + mean);
 
            System.out.println("The standard deviation is " + deviation);
 
    }
 
public static double sum(double[] a) {
        double sum = 0.0;
        for (int i = 0; i < a.length; i++) {
            sum += a[i];
        }
        return sum;
    }
 
 
 
 
 
 
 
    public static double mean(double[]x, double i){
 
        if (x.length == 0) return Double.NaN;
        double sum = sum(x);
        return sum / x.length;
    }
 
 
 
 
 
 
    public static double var(double[] x) {
        if (x.length == 0) return Double.NaN;
        double avg = mean(x, 10);
        double sum = 0.0;
        for (int i = 0; i < x.length; i++) {
            sum += (x[i] - avg) * (x[i] - avg);
        }
        return sum / (x.length - 1);
    }
 
 
}

I am not sure if my code is just wrong, if I am using the incorrect formula for standard deviation, or both. I've been working on this all freakin day and my head is about to explode. I suck at this stuff. If anyone can help I'd really appreciate it.

return sum / (x.length - 1);

You forgot to take the square root.