private void generateButton_Click(object sender, EventArgs e)
    {
        // Create an array to hold the numbers.
        const int SIZE = 5;
        int[] lotteryNumbers = new int[SIZE];

        // Create a Random object.
        Random rand = new Random();

        // Fill the array with random numbers, in the range // of 0 through 99.
        for (int index = 0; index < lotteryNumbers.Length; index++)
        {
            lotteryNumbers[index] = rand.Next(100);
        }

        // Display the array elements in the Label controls.
        firstLabel.Text = lotteryNumbers[0].ToString();
        secondLabel.Text = lotteryNumbers[1].ToString();
        thirdLabel.Text = lotteryNumbers[2].ToString();
        fourthLabel.Text = lotteryNumbers[3].ToString();
        fifthLabel.Text = lotteryNumbers[4].ToString();
    }

    private void exitButton_Click(object sender, EventArgs e)
    {
        // Close the form.
        this.Close();
    }

declare resultVariable

loop all numbers in lotteryNumbers
   add current number in lotteryNumbers to resultVariable