C＃如何根据字典的键将字典的值添加到变量中？

Question

I have to calculate the price of an order based on the input from the user using a Dictionary, but I can't seem to get it right.

1. Chicken Strips - $3.50
2. French Fries - $2.50
3. Hamburger - $4.00
4. Hotdog - $3.50
5. Large Drink - $1.75
6. Medium Drink - $1.50
7. Milk Shake - $2.25
8. Salad - $3.75
9. Small Drink - $1.25

For example, if the input is 236, the price of the order should be $8.

Converting my LINQ query to double didn't work (my query is also definitely wrong). I don't really know any LINQ but as you can't really use a for loop for a dictionary as they aren't indexed, I don't really have any other choice.

        Dictionary<int, double> items = new Dictionary<int, double>()
        {
            { 1, 3.50 },
            { 2, 2.50 },
            { 3, 4.00 },
            { 4, 3.50 },
            { 5, 1.75 },
            { 6, 1.50 },
            { 7, 2.25 },
            { 8, 3.75 },
            { 9, 1.25 }
        };

        string order = Console.ReadLine();
        double sum = 0;
        for (int i = 0; i < order.Length; i++)
        {
            sum += Convert.ToDouble(items.Where(x => x.Key == int.Parse(order[i].ToString())).Select(x => x.Value));
        }
        Console.WriteLine(sum);
        Console.ReadKey();

Well, the output should be the correct amount of dollars based on the input from the user.

Answer 1

无需循环。

var sum = order.Sum(c => items[int.Parse(c.ToString())]);

Answer 2

This implementation is quite fragile, it only allows 10 items and relies on string parsing but I think the following code does what you're asking:

order.Sum(character =>
{
    int id = character - '0';

    return items.TryGetValue(id, out double price) ? price : 0d;
});

TryGetValue checks that order only contains digits which are keys in the items dictionary.

Answer 3

尝试这个

order.Select(c => (c - '0')).Where(c => c > 0 && c < 10).Sum(c => items[c])

Answer 4

You can use sum += items[order[i]-'0']; in your for loop.

This works because '0' is stored with the value 48 (see the answers to this question ). The rest of the digits are stored in order ('1' is 49, '2' is 50, etc), so '1' - '0' == 1 and so forth.