Check for missing number in sequence

Question

I have an List which contains 1,2,4,7,9 for example.

I have a range from 0 to 10.

Is there a way to determine what numbers are missin

Answer 1

 int sum = 0,missingNumber;
        int[] arr = { 1,2,3,4,5,6,7,8,9};
        for (int i = 0; i < arr.Length; i++)
        {
            sum += arr[i];
        }
        Console.WriteLine("The sum from 1 to 10 is 55");
        Console.WriteLine("Sum is :" +sum);
        missingNumber =  55 - sum;
        Console.WriteLine("Missing Number is :-"+missingNumber);
        Console.ReadLine();