Question

我需要能够显示每年有多少注册学生。所以我有一个名为School的课程，其中学生在课堂上创建的对象可以注册到特定的学校，不知道如何做到这一点。我试图学习OOP，因为我没有在Uni中这样做并且必须教它。我知道这可能是一个简单的问题，但现在已经尝试了一周，而且很简单。代码如下：

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

namespace objects2
{
class Program
{
    static void Main()
    {
        Student jack = new Student();
        jack.setName("Jack");
        jack.setStudentNumber(1);
        jack.setYearLevel(13);
        Student jane = new Student();
        jane.setName("Jane");
        jane.setStudentNumber(2);
        jane.setYearLevel(10);
        Student Amy = new Student();
        Amy.setName("Amy");
        Amy.setStudentNumber(3);
        Amy.setYearLevel(10);
        Student Ezekeil = new Student();
        Ezekeil.setName("Ezekiel");
        Ezekeil.setStudentNumber(4);
        Ezekeil.setYearLevel(9);
        Student Burt = new Student();
        Burt.setName("Burt");
        Burt.setStudentNumber(5);
        Burt.setYearLevel(9);
        Student Ernie = new Student();
        Ernie.setName("Ernie");
        Ernie.setStudentNumber(6);
        Ernie.setYearLevel(11);
        Student James = new Student();
        James.setName("James");
        James.setStudentNumber(7);
        James.setYearLevel(11);

        School CHBC = new School();
        CHBC.enrol(Amy);
        CHBC.enrol(jack);
        CHBC.enrol(jane);
        CHBC.enrol(Ezekeil);
        CHBC.enrol(Burt);
        CHBC.enrol(Ernie);
        Console.WriteLine(" Number enrolled: " + CHBC.countEnrolled);
        Console.ReadKey();
    }
}
class Student
{
    private string name;
    private int studentNumber;
    private int yearLevel = 9;

    public int setYearLevel(int yearLevel)
    {
        if (yearLevel <= 13 && yearLevel >= 9)
        {
            //talking about the variable in the class by using this to stop having to reinvent names
            this.yearLevel = yearLevel;
            return 0;
        }
        //error codes so can have specific error otherwise could use boolean for OK or not OK
        return -1;
    }
    public int showYearLevel()
    {
        return yearLevel;
    }
    public void setStudentNumber(int studentNumber)
    {
        this.studentNumber = studentNumber;
    }
    public int showStudentNumber()
    {
        return studentNumber;

    }
    public void setName(string name)
    {
        this.name = name;
    }
    public string showName()
    {
        return name;
    }
}

class School
{
    private string schoolName;
    private string type;
    private List<Student> students = new List<Student>;
    private int numberEnrolled;


    public void enrol(Student newStudent)
    {
        //add students to my list as they arre enrolled
        students.Add(newStudent);

    }
    public void setSchoolName(string schoolName)
    {
        this.schoolName = schoolName;
    }

    public int countEnrolled
    {
        get
        {
            numberEnrolled = students.Count();
            return numberEnrolled;
        }
    }
    public void setType(string type)
    {
        this.type = type;
    }

}

}

提前致谢。

Answer 1

那Student课很可怕。从这样的事情开始：

class Student
{
    public int Number { get; private set; }
    public string Name { get; private set; }
    public int YearLevel { get; private set; }

    const int yearLevelMin = 9;
    const int yearLevelMax = 13;

    public Student(int number, string name, int yearlevel)
    {
        if (string.IsNullOrWhiteSpace(name))
            throw new ArgumentNullException(nameof(name));

        if (yearlevel < yearLevelMin || yearlevel > yearLevelMax)
            throw new StudentException($"{nameof(yearlevel)} must be between {yearLevelMin} and {yearLevelMax}.");

        Number = number;
        Name = name;
        YearLevel = yearlevel;
    }
}

让您的基础课程先行。我不会为你写School课程，但你应该可以这样做：

var school = new School("Example High")
    .Add(new Student(1, "Jack", 13))
    .Add(new Student(2, "Jane", 10));

Answer 2

我将跳过一些细节，然后直接回答你的问题。

首先，您需要拥有属性的公共访问者。

public class Student
{
   public int Number { get; set; }
   public string Name { get; set; }
   public int YearLevel { get; set; }
}

public class School
{
   public string Name { get; set; }
   public string Type { get; set; }
   public List<Student> Students { get; set; }
}

然后您可以按年级计算学生人数。

// this is using Linq
int numberOfStudents = Students.Count(s=>s.YearLevel == yearLevelYouAreLooking);

但是你想要显示每年级别的计数，所以你需要的是按年级对学生进行分组并获得计数。

 // school is School instance
 var result = from student in school.Students // from all students in the school
              group student by student.YearLevel into g // group the students by the YearLevel
              select new { YearLevel = g.Key, Count = g.Count() } // create a new list of YearLevel and the count.

将结果显示在控制台

中

foreach(var item in result)
{
   Console.WriteLine($"Number of students of {item.YearLevel} is {item.Count}");
}

您可以根据需要将它们作为课程的方法。

注意：结果不在订单中。如果您需要订购结果，请添加：

orderby student.YearLevel // in between "from" and "group", but this is not optimal, because you are re-ordering the input first, which can be large.

或

orderby g.Key // in between "group" and "select". Since the grouped result will be smaller than the input, ordering is optimal.

从不同的类访问对象参数？

2 个答案: