In c#----how to create a "class object" as array.....?

Question

1.00/5 (1 vote)

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

What I have tried:

C#

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);
    }
}

Posted 3-Mar-16 7:23am

Member 12367751

Updated 3-Mar-16 7:42am

Sascha Lefèvre

v2

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2 solutions

Solution 2

Hi, the problem is, you just created an array for holding objects of type Students, you didn't assign student objects to that array, the array is empty. so just instantiate the array by assigning student object. change the code as follows inside main,

C#

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();

Posted 3-Mar-16 7:42am

VR Karthikeyan

Comments

Sascha Lefèvre 3-Mar-16 14:41pm

Basically right but a bit inefficient to not use a for-loop for the array initialization ;) +4

VR Karthikeyan 3-Mar-16 23:07pm

thanks, you are right.

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Sascha Lefèvre · Accepted Answer · 2016-03-03T07:35:00

On this line:

C#

s[i].getvals();

..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:

C#

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

(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.