关于索引器的问题
以下代码编译的时候为什么会出现未将对象引用设置到对象的实例呢？
帮忙给解释下谢谢
using System;
class Average
{
private double _avg;
public double avg
{
set{_avg=value;}
get{return _avg;}
}
}

class IndexForAverage
{

Average [] avgs=new Average[4];


public double this[int year]
{
set
{
if(year <=0 || year> 4)
{
Console.WriteLine( "年级无效！ ");
return ;
}
int index=year-1;

avgs[index].avg=value;
}
get
{
if(year <=0 || year> 4)
{
Console.WriteLine( "年级无效！ ");
return -1;
}
int index=year-1;
return avgs[index].avg;
}
}
}

class TestIndex
{
public static void Main()
{
IndexForAverage ifa=new IndexForAverage();

ifa[1]=2.33;
ifa[2]=3.22;

Console.WriteLine(ifa[1].ToString());


}
}

[解决办法]
未赋值
[解决办法]
Average [] avgs=new Average[4];
构造函数里

for( int i=0 ; i <4 ; i++ )
{
avgs[i] = new Average();
}