收到错误消息“未获得最大值和最小值”

Question

如何纠正此代码？请帮忙。该代码包含数组，我想找到最大和最小数量。

发生此错误：

未处理的异常：System.NullReferenceException：对象引用未设置为对象的实例。    在D：\ C＃\ assign 3.1 \ assign 3.1 \ Program.cs：line 62中的Assign_3._1.ArrayOperations.Maximum（）    在D：\ C＃\ assign 3.1 \ assign 3.1 \ Program.cs：line 97中的assign_3._1.Program.Main（String [] args）

class Numbers
{ 
    public int iSize;
    public int[] arr;

    public Numbers()
    {
    }

    public Numbers(int x)
    {
        iSize = x;
        arr = new int[iSize];
    }

    public Numbers(Numbers obj)
    {
        iSize = obj.iSize;
        arr = obj.arr;
    }

    public void Accept()
    {
        int i = 0;
        Console.WriteLine("Enter Elements");
        for (i = 0; i < iSize; i++)
        {
            arr[i] = Convert.ToInt32(Console.ReadLine());
        }
    }

    public void Display()
    {
        int i = 0;
        for (i = 0; i < iSize; i++)
        {
            Console.WriteLine("{0}", arr[i]);
        }
    }
}

class ArrayOperations : Numbers
{
    public int Maximum()
    {
        int i = 0;
        int iMax = 0;

        iMax = arr[0];

        for (i = 0; i < iSize; i++)
        {
            if (arr[i] > iMax)
            {
                iMax = arr[i];
            }
        }

        return iMax;
    }

    public int Minimum()
    {
        int i = 0;
        int iMin = 0;
        iMin = arr[0];

        for (i = 0; i < iSize; i++)
        {
            if (arr[i] < iMin)
            {
                iMin = arr[i];
            }
        }
        return iMin;
    }
}

class Program
{
    static void Main(string[] args)
    {
        Numbers obj = new Numbers();
        obj.Accept();

        Numbers obj1 = new Numbers(5);
        obj1.Accept();
        obj1.Display();

        Numbers obj2 = new Numbers(obj1);
        obj2.Accept();
        obj2.Display();

        ArrayOperations obj3 = new ArrayOperations();
        obj3.Maximum();
        Console.WriteLine("Maximum Number is{0}", obj3.Maximum());
        obj3.Minimum();
        Console.WriteLine("MInimum Number is{0}", obj3.Minimum());
    }
}