什么是大型开关盒的良好替代品？

Question

I have objects called Country. At some point in the program, I want to set the field power of each object.

The power for each country is fixed and I have data for all 196 countries here on a piece of paper. My code should check, for instance, if the country's name is USA (and if so, set its power to 100) and so on.

I know I can do it with a switch-case, but what is the best, nicest, and most efficient way to do it?

Answer 1

You can store country-power pairs into a Dictionary<string, int> then just get the score of a particular country by using indexer:

var points = new Dictionary<string,int>();
// populate the dictionary...
var usa = points["USA"];

Edit: As suggested in comments you should store the information in external file, for example an xml would be a good choice. That way you don't have to modify the code to add or remove countries. You just need to store them into XML file, edit it whenever you need.Then parse it when your program starts, and load the values into Dictionary .You can use LINQ to XML for that.If you haven't use it before there are good examples in the documentation to get you started.

Answer 2

Whilst Selmans answer is right and good, it does not answer how to actually populate the Dictionary. Here is it:

var map = new Dictionary<string, int> {
    {"USA", 100},
    {"Germany", 110}
};

you may however also just add it as follows:

map.Add("USA", 100);
map.Add("Germany", 110);

Now you may access the value (as already mentioned by Semans):

map["USA"] = 50;        // set new value for USA
int power = map["USA"]; // get new value

EDIT: As already mentioned within comments and other answers you may of course store the data within an external file or any other data-storage. Having said this you may just initialize an empty dictionary and then fill it with the Add-method previously mentioned for every record within that storage.

Answer 3

This is the right question to begin with, but there are a lot of things you need to learn. Many folk have given you answers to the question you asked. I'm going to be annoyingly Zen and tell you to unask the question because there is a larger problem to resolve.

Instead of hard coding this, store the related properties in an n-tuple also known as a database row and use a database engine to manage the relation between the two. And then since you are using C# it would probably be smart to learn to use LINQ. But before you do that, learn a bit of data modelling theory, because data-modelling is what you are doing.

Answer 4

Since you said you have "objects" called "Country", and you have tagged your question "C#", it would seem that you have two forces at work in your code. One is that having to refer to a map, however efficiently implemented, is not as cheap as referring to a member variable . On the other hand there might be some benefit to a setup where all the attributes of a country can be found in the same place as the attributes of other countries (the map-oriented solutions do address this concern). But these forces can be reconciled something like this:

class Country { // Apologies that this sketch is more C++ than C#
public:
   Country(string name_, int power_);
private:
   string name;
   int power;
};
void MakeCountries()
{
    countries.Add(new Country("USA", 50));
    countries.Add(new Country("Germany", 60));
    // ....
}

Answer 5

Do you need to update your data at runtime?

• Yes? Load data from external storage into a dictionary.

• No? Use a switch

  Let the compiler generate dictionaries and hash-based lookups for you. When you profiler starts screaming, explore alternative solutions. For example, read that answer from " What is quicker, switch on string or elseif on type? ".

Answer 6

What about making an array of Strings for storing country names in ascending order of their power. It will be more simple to implement.Then the index of each country can represent its power. This is possible, only if the power is continues counting numbers.

If its not , another siple way is to implement them as linked list. So that u will be able to change if u want. A list with 2 fields; 1for the country and other for the power