通过索引从数组中删除字符串

Question

I'm trying to build a simple country capitals quiz program using c#. Currently, I am giving the user a random country from the countries list and asking for input on what the capital is. Then there is a conditional that checks if the correct capital is equal to the input. After this completes, I need to be able to remove the country and capital asked from each array so that the loop does not repeat them. Here is the code I have so far:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;

namespace program {
  class MainClass {
    public static void Main (string[] args) {
      string[] countries = new string[] {"Germany", "Poland", "France", 
                                        "United States", "Russia", "Japan"};
      string[] capitals = new string[] {"berlin", "warsaw", "paris", 
                                       "washington dc", "moscow", "tokyo"};

      int score = 0;
      int length = countries.Length;

      string current_country = countries[random_number];
      string current_capital = capitals[random_number];

      for (int i = 0; i <= length;) {
        Random rnd = new Random();
        int random_number = rnd.Next(0, length);
        Console.WriteLine("What is the capital of {0}?", current_country);
        string capital_input = Console.ReadLine();

        if (capital_input == current_capital) {
          Console.WriteLine("Correct!");
          countries.Remove[random_number];
          capitals.Remove[random_number];
          score += 1;
          continue;
        } else {
          Console.WriteLine("Incorrect!");
          countries.Remove[random_number];
          capitals.Remove[random_number];
          continue;
      }

      if (length == 0) {
        break;
      }
    }

    int score_percent = score * 20;
    Console.WriteLine("Congratulations! You scored {0}% of questions 
                      correct.", score_percent);
  }
}

}

The program fails to compile with these errors:

exit status 1
main.cs(27,34): error CS0201: Only assignment, call, increment, decrement, 
await, and new object expressions can be used as a statement
main.cs(28,28): error CS0201: Only assignment, call, increment, decrement, 
await, and new object expressions can be used as a statement
main.cs(33,29): error CS0201: Only assignment, call, increment, decrement, 
await, and new object expressions can be used as a statement
main.cs(34,28): error CS0201: Only assignment, call, increment, decrement, 
await, and new object expressions can be used as a statement
Compilation failed: 4 error(s), 0 warnings

Any ideas?

Answer 1

Consider using the following:

List<string> remainingCountries = new List<string>(){ "US", "Germany", "Russia"};
void RemoveIncorrectGuess(string countryToRemove)
{
   remainingCountries.Remove(countryToRemove);
}

Answer 2

There are many issues in your code. If you want working code then use this:

 public static void Main(string[] args) {
    List<string> countries = new List<string> { "Germany", "Poland", "France", "United States", "Russia", "Japan" };
    List<string> capitals = new List<string> { "berlin", "warsaw", "paris", "washington dc", "moscow", "tokyo" };

    int score = 0;
    Random rnd = new Random();

    while(countries.Count > 0) {
        int random_number = rnd.Next(0, countries.Count);

        string current_country = countries[random_number];
        string current_capital = capitals[random_number];

        Console.WriteLine("What is the capital of {0}?", current_country);

        string capital_input = Console.ReadLine();

        if (!string.IsNullOrWhiteSpace(capital_input) && capital_input.Equals(current_capital, StringComparison.InvariantCultureIgnoreCase)) {
            Console.WriteLine("Correct!");
            score++;
        } else {
            Console.WriteLine("Incorrect!");
        }
        countries.RemoveAt(random_number);
        capitals.RemoveAt(random_number);
    }

    int score_percent = score * 20;
    Console.WriteLine("Congratulations! You scored {0}% of questions correct.", score_percent);
    Console.ReadKey();
}

Now I try to explain some cases (also using comments):

1. You can't remove elements from arrays using Remove[random_number] . As said J.Skeet: Remove is a method, not an indexer
2. It would be better to use List<string> instead. Then you can remove elements like RemoveAt(random_number)
3. You're using random_number before you've declared it.
4. Don't declare the Random in the loop.
5. In this case using while instead of for is more preferable
6. Check of input capital with ignore case