private void btnCalculate_Click(object sender, EventArgs e)
{
int startNumber;
int endNumber;
if (int.TryParse(txtStartNumber.Text, out startNumber) && int.TryParse(txtEndNumber.Text, out endNumber))
{
int sum = 0;
for (int i = startNumber; i <= endNumber; i++)
{
sum += i;
}
lblResult.Text = "Toplam: " + sum.ToString();
}
else
{
MessageBox.Show("Geçerli sayılar girin.");
}
}