Standard deviation

Question

I need to calculate standard deviation , and I cant figure out how to do it =(
I have all kind of variables you need, average of all numbers , sum of all numbers.

        int sum=0;

        int average = 0;

        int highestNumber = 0;

        int lowestNumber = 0;

        final int  matchedNumber = 500;

        final int lessThan = 1000;

        boolean found = false;

        int countLessThan= 0;

        int countAverage = 0;

        

        int limit = 10000;

        int[] array = new int[limit];

        

        Random gen = new Random();

        

        for(int index=0; index < array.length; index++)

        {

            // random values generated

            array[index] = gen.nextInt(10001 - 1+ 1) + 1;

            // sum of all numbers in array

            sum += array[index];

            // average of all numbers

            average = sum / array.length;

            //Highest number

           if(array[index]> highestNumber)

           {

               highestNumber = array[index];

           }

           if(array[index] < lowestNumber)

           {

               lowestNumber = array[index];

           }

            

           if(matchedNumber == array[index])

           {

               found = true;

           }

           if(array[index]< lessThan)

           {

               countLessThan++;

           }

           if(array[index]<average)

           {

               countAverage++;

           }

                  

            

        }

        System.out.println("The sum of all numbers is "+sum);

        System.out.println("The average of all numbers is "+average);

        System.out.println("The highest number is "+highestNumber);

        System.out.println("The lowest number is "+lowestNumber);

        System.out.println("Is there a numer 500 in array? "+found);

        System.out.println("There are  "+countLessThan+" numbers less than 1000");

        System.out.println("There are "+countAverage+" numbers less than average");