List<> 不能使用 C#

Question

I have this error and I don't have any idea what's happening, I'm new learning C# and where I'm learning they use this:

using System;

namespace AgentSmith
{
    class AgentSmith_missions
    {
        public static void Main(string[] args)
        {
            double[] array = {1.1, 2.2, 3.3};
            List<double> times  = new List<double>();
            times.Add(4.20);
            times.Add(7.30);
            times.Insert(1, 9.35);
            var four = times.IndexOf(4.20);
            times.Remove(times[four]);
            double seven = times.Contains(7.30);
            string s = String.Join(", ", times);
            Console.WriteLine(s + seven);
       }
    }
}

The console error is this:

/Users.../AgentSmith.cs(10,13): error CS0246: The type or namespace name 'List<>' could not be found (are you missing a using directive or an assembly reference?)    
/Users.../AgentSmith.cs(10,39): error CS0246: The type or namespace name 'List<>' could not be found (are you missing a using directive or an assembly reference?)

Answer 1

Here is a keyboard shortcut that'll make this easier to fix:

Control .

That is, the Control key plus the period . key.

That keyboard shortcut tries to resolve the item under the cursor, which often is a matter of adding a using to bring a namespace into scope. If you get an error squiggly on something that you know is defined, click on it and hit Control . and look for the missing namespace.

Answer 2

要添加这个using在你的类的顶部：

using System.Collections.Generic;

Answer 3

You have coded for a list in your Main function. But you also need to add a reference to the List class so that your compiler knows what to do with List . Just add the following to the top of your file:

using System.Collections.Generic;

In addition, it looks like this line could cause a problem as well:

double seven = times.Contains(7.30);

Contains returns a bool . It's true or false based on whether or not the list contains that value. What you are probably looking for here is First , which returns the first value that matches:

double seven = times.First(x => x == 7.30);

Answer 4

You have to add System.Collections.Generic; add also times.Contains(7.30); return a booleen not a double.