在c＃中----如何创建“类对象”作为数组.....？

问题描述

我尝试了下面这段代码，但是显示错误就像system.nullreference异常对象没有设置为......等等。



什么我试过了：

i tried this below code but its showing error Like system.nullreference Exception object not set to......etc..

What I have tried:

using System;
class _8__CreatingObjectAsArray
{
   static int i;
    static void Main(string[] args)
    {
        students[] s = new students[5];
        //for (int i = 0; i < s.Lengts; i++)
        //    s[i] = new students[5];
        Console.WriteLine(s.Length);
        for (i = 0; i < s.Length; i++)
            s[i].getvals();

        for (i = 0; i < s.Length; i++)
            s[i].display();
    }
}
class students
{
    private int rno, marks;
    private string sname;
    public void getvals()
    {
        Console.WriteLine("enter roll no of student...");
        rno = int.Parse(Console.ReadLine());
        Console.WriteLine("enter name of student...");
        sname = Console.ReadLine();
        Console.WriteLine("enter marks of student...");
        marks = int.Parse(Console.ReadLine());
    }
    public void display()
    {
        Console.WriteLine("roll no = "+rno+"stu name = "+sname+"marks = "+marks);
    }
}

推荐答案

s[i].getvals();

..你试图访问学生 -object在数组中，但还没有。此时的数组只包含空值，所以你在这里得到了空引用异常。



我假设你已经注释掉了for循环应该是这样的：

..you're attempting to access a students-object in the array but there is none yet. The array at this point contains nothing but nulls, so you're getting the null-reference exception here.

I assume the for-loop which you've commented out should look like this:

for (int i = 0; i < s.Length; i++)
       s[i] = new students();

（然后将分配一个新的学生 -object每个数组索引。）



旁注：在C＃中，类名和方法名应为CamelCase，并作为学生的一个对象代表一个学生，我建议将课程命名为学生。方法：显示和 GetVals 或 GetValues 。

(Which then will assign a new students-object to each array-index.)

Sidenote: In C#, class names and method names should be "CamelCase" and as one object of students represents one student, I suggest to name the class Student instead. And the methods: Display and GetVals or GetValues.

students[] s = new students[5];
s[0] = new students();
s[1] = new students();
s[2] = new students();
s[3] = new students();
s[4] = new students();
//for (int i = 0; i < s.Lengts; i++)
//    s[i] = new students[5];
Console.WriteLine(s.Length);
for (i = 0; i < s.Length; i++)
    s[i].getvals();

for (i = 0; i < s.Length; i++)
    s[i].display();

Console.ReadLine();

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