从列表中取出一项并将其导入另一个列表

Question

所以，长话短说，我想把缺席的人只导入缺席名单，每次我尝试这样做时，它都会从学生名单中导入所有人，所以没有多大帮助；

这样在最后我可以清除并显示每个学生的出勤颜色，如果他们缺席，则为红色，如果他们在场，则为绿色

提前 :)

using System.Collections.Generic;

namespace HelloWorld
{
    class Hello
    {
        static void Main(string[] args)
        {
            List<string> students = new List<string>(5);
            students.Add("Obama Ojane"); 
            students.Add("Yarik Ze");
            students.Add("Allen O'neill");
            students.Add("Naveen Sharma");
            students.Add("Monica Rathbun");
            students.Add("David McCarter");
            students.Add("Zayne Pan");
            students.Add("Rah");

            int v = 0;
            int abs = 0;
            int pres = 0;

            List<string> absent = new List<string>(5);
            List<string> present = new List<string>(5);

            foreach (string a in students)
            {
                Console.Write(students[v] + ": ");
                string attendance = Console.ReadLine();
                if (attendance == "absent" || attendance == "abs" || attendance == "a")
                {
                    abs++; 
                    absent.Append(attendance);
                    String studentNameA = students[v];
                    absent.Add(studentNameA);
                }
                if (attendance == "present" || attendance == "pres" || attendance == "p")
                {
                    pres++;
                    present.Append(attendance);
                    String studentNameP = students[v];
                    absent.Add(studentNameP);

                }
                v++;
            }
            Console.WriteLine();
            Console.Clear();
            Console.WriteLine("total present: " + pres);
            Console.WriteLine("total absent: " + abs);
            Console.WriteLine("total students: " + (abs+pres));



            Console.ForegroundColor = ConsoleColor.Red;
            for (int i = 0; i < absent.Count; i++)
            {
                Console.WriteLine(absent[i]);
            }

            Console.ForegroundColor = ConsoleColor.Green;
            for (int i = 0; i < present.Count; i++)
            {
                Console.WriteLine(present[i]);
            }

        }
    }
}

Answer 1

复制 + 粘贴是邪恶：absent.Add(studentNameP); as UnholySheep 放入 cmets 绝对是个问题。

让我们实现例程：

我们从数据开始：

// Keep it simple with a help of syntax sugar
var students = new List<string>() {
  "Obama Ojane",
  "Yarik Ze",
  "Allen O'neill",
  "Naveen Sharma",
  "Monica Rathbun",
  "David McCarter",
  "Zayne Pan",
  "Rah",
};

// avoid magic constants: what did 5 stand for? 
var absent = new List<string>(students.Count);
var present = new List<string>(students.Count);

然后我们添加UI，我们将学生分配到absent 或present：

foreach(var student in students) {
  // List (either present or absent) in which we add 
  List<string> list = null;

  // Keep asking user until absent or present is selected
  do {
    Console.Write($"{student}: ");

    string attendance = Console.ReadLine().Trim();

    if (attendance == "absent" || attendance == "abs" || attendance == "a")
      list = absent;  // we add to absent
    else if (attendance == "present" || attendance == "pres" || attendance == "p")
      list = present; // we add to present
  }
  while (list == null); 

  list.Add(student);
}

最后，我们输出：

Console.Clear();
Console.WriteLine($"total present:  {present.Count}");
Console.WriteLine($"total absent:   {absent.Count}");
Console.WriteLine($"total students: {present.Count + absent.Count}");

Console.ForegroundColor = ConsoleColor.Red;

foreach (var student in absent)
  Console.WriteLine(student);

Console.ForegroundColor = ConsoleColor.Green;

foreach (var student in present)
  Console.WriteLine(student); 

Answer 2

您的一个问题是您试图让一种方法Main() 做得太多。如果你把事情分解成每个做一件事的离散方法，事情就会变得简单得多。也更容易理解：

using System.Collections.Generic;

namespace HelloWorld
{
  class Hello
  {
      static void Main(string[] args)
      {
        List<string> students = new List<string>(new string[]{
          "Obama Ojane",
          "Yarik Ze",
          "Allen O'neill",
          "Naveen Sharma",
          "Monica Rathbun",
          "David McCarter",
          "Zayne Pan",
          "Rah",
        });
        List<string> absent = new List<string>();
        List<string> present = new List<string>();

        foreach (string student in students)
        {
          bool isPresent = getStatus(student);
          if (isPresent)
          {
            present.Add(student);
          }
          else
          {
            absent.Add(student);
          }
        }

        WriteSummary(present.Count, absent.Count, students.Count);
        WriteReport(absent, "Absent", ConsoleColor.Red);
        WriteReport(present, "Present", ConsoleColor.Green);

      }

      static void WriteSummary(int present, int absent, int total)
      {
        Console.Clear();
        Console.WriteLine("total present: {0}", present);
        Console.WriteLine("total absent: {0}", absent);
        Console.WriteLine("total students: {0}", students);
      }

      static void WriteReport(List<string> students, string title, ConsoleColor color)
      {
        Console.WriteLine();
        Console.WriteLine("{0}:", title);
        Console.ForegroundColor = color;
        foreach (var student in students)
        {
            Console.WriteLine(student);
        }
      }

      static bool getStatus(string student)
      {

        // loop forever
        while (true)
        {

          // prompt with the student's name
          Console.Write("{0}: ", student);

          // read the response
          string status = Console.ReadLine();

          // test the response
          switch (status.ToLower())
          {
          case "a":
            // student is absent
            return false;
          case "p":
            // student is present
            return true;
          default:
            // otherwise, the response is is incorrect/unknown.
            // report the error and prompt again
            Console.WriteLine("Please enter 'a' for absent or 'p' for present");
          }

        }

      }

  }

}