使用C＃进行分配以应用折扣。 我正在使用if-else

Question

My assignment is:

Each item sold is $99.

You get no discount selling under 10, so 1-9.

You get a 5% discount selling 10-19.

You get a 10% discount selling 20+.

When I put 1-9 numbers in my textbox, it doesn't apply the discount which is good. When I put 10-19, it applies the 5% off discount. But when I put 20 or any numbers higher, it still applies the 5% off discount and not a 10% discount.

My code:

double dblQuantitySold;
double dblAmountTotalDue;
double dblPrice = 99;

//Acquire the math.
dblQuantitySold = double.Parse(txtQuantity.Text);
dblAmountTotalDue = dblQuantitySold * dblPrice;

//Create the solution for your if-else statement.
if (dblQuantitySold >= 10)
{
    dblAmountTotalDue -= dblQuantitySold * dblPrice * 0.05;
    MessageBox.Show("A 5% discount will be given because 10 or more has been sold.");
}
else if (dblQuantitySold >= 20)
{
    dblAmountTotalDue -= dblQuantitySold * dblPrice * 0.10;
    MessageBox.Show("A 10% discount will be given because 20 or more has been sold.");
}

//Display the results.
lblAmountDueTotal.Text = dblAmountTotalDue.ToString("C");

Answer 1

Do this instead. Add additional conditional operator on your first if which will react as between two number condition.

if (dblQuantitySold >= 10 && dblQuantitySold < 20)
{
    dblAmountTotalDue -= dblQuantitySold * dblPrice * 0.05;
    MessageBox.Show("A 5% discount will be given because 10 or more has been sold.");
}

Answer 2

It's because you have the if statements in the wrong order. You first check if the item is greater than or equal to 10, which includes all values greater than 20. Just put the check for >=20 first:

if (dblQuantitySold >= 20)
{
    dblAmountTotalDue -= dblQuantitySold * dblPrice * 0.10;
    MessageBox.Show("A 10% discount will be given because 20 or more has been sold.");
}
else if (dblQuantitySold >= 10)
{
    dblAmountTotalDue -= dblQuantitySold * dblPrice * 0.05;
    MessageBox.Show("A 5% discount will be given because 10 or more has been sold.");
}

Answer 3

Try this:

if (dblQuantitySold >= 20)
{
    dblAmountTotalDue -= dblQuantitySold * dblPrice * 0.10;
    MessageBox.Show("A 10% discount will be given because 20 or more has been sold.");
}
else if (dblQuantitySold >= 10)
{
    dblAmountTotalDue -= dblQuantitySold * dblPrice * 0.05;
    MessageBox.Show("A 5% discount will be given because 10 or more has been sold.");
}

Your conditions were in the wrong order.

If you want to go for bonus points try this code:

decimal price = 99;

decimal quantitySold = decimal.Parse(txtQuantity.Text);

var discounts = new[]
{
    new { percentage = 0.0m, threshold = 0 },
    new { percentage = 0.05m, threshold = 10 },
    new { percentage = 0.1m, threshold = 20 },
};

var discount =
    discounts
        .OrderBy(d => d.threshold)
        .Where(d => d.threshold <= quantitySold)
        .Last();

decimal amountTotalDue = quantitySold * price * (1m - discount.percentage);

if (discount.percentage > 0m)
{
    var message = String.Format(
        "A {0:0%}% discount will be given because {1} or more has been sold.",
        discount.percentage,
        discount.threshold)

    MessageBox.Show(message);
}

lblAmountDueTotal.Text = amountTotalDue.ToString("C");

The advantage here is that you separate the discount structure from the code that computes the discount. This allows you to then extract away the discounts into a file or database and allow the application to be easily customizable.