c#如何为foreach语句中的空值赋值？
using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication2
{
class Program
{
static void Main(string[] args)
{
//Program mytest = new Program();
//Console.WriteLine(testing());

testing();
}

private static string testing()
{
//string sum = "";
string[] arr = new string[5];
arr[1] = "5";
arr[3] = "51";
arr[4] = "52";
foreach (string i in arr)
{
if (i=="")
{
i="空";
}

Console.WriteLine(i);

}
//return sum;
return arr.ToString();
}
}
}

调试的结果出错
提示为：“i是一个foreach变量，无法为它赋值”

[解决办法]
for (int i =0；i<arr.lenght,i++)
{
if (arr[i]=="")
{
arr[i]="空";
}

Console.WriteLine(i);

}

[解决办法]
string[] arr = new string[5];
arr[1] = "5";
arr[3] = "51";
arr[4] = "52";
int ii = 0;
foreach (string i in arr)
{
if (i == "")
{
arr[ii] = "空";
}
ii++;
}
[解决办法]
string[] arr = new string[5];
arr[1] = "5";
arr[3] = "51";
arr[4] = "52";
arr = (from string _string in arr select (_string ==null?"空":_string)).ToArray();