C#循环替换的有关问题。代码该如何写

C#循环替换的问题。代码该怎么写
现有一文本，里面内容大致为

10000
10000
10000
10000


想要替换为

10001
10002
10003
10004

注意，是替换，不是生成。
代码该怎么写啊

[解决办法]

C# code

            string[] lines = File.ReadAllLines("读取文件路径");            for (int i=0; i < lines.Length;i++)            {                lines[i] = (int.Parse(lines[i]) + i+1).ToString();                Console.WriteLine(lines[i]);            }            File.WriteAllLines("写入文件路径",lines);
[解决办法]
C# code
string pattern_line = @"(?<=\d+?)\d(?=\s|$)";            string[] text_lines = File.ReadAllLines(@"C:\Users\M\Desktop\Test.txt", Encoding.GetEncoding("GB2312")).Select((a, i) => {                a = Regex.Replace(a, pattern_line, (i + 1).ToString());                return a;             }).ToArray();//读取并替换            File.WriteAllLines(@"C:\Users\M\Desktop\Test.txt",text_lines);//写回txt
[解决办法]
C# code
        int counter = 1;        string s = File.ReadAllText((@"c:\test.txt"));        string r = Regex.Replace(s, @"(?m)\d+", delegate(Match match)        {            int value = int.Parse(match.Value) + counter++;            return value.ToString();        });        File.WriteAllText((@"c:\test.txt"), r);
[解决办法]
C# code
string[] text_lines = File.ReadAllLines(@"C:\Documents and Settings\Administrator\桌面\Test.txt", Encoding.GetEncoding("GB2312")).Select((a, i) =>        {            a = a.Replace("@",(i + 1).ToString());            return a;        }).ToArray();//读取并替换        File.WriteAllLines(@"C:\Documents and Settings\Administrator\桌面\Test.txt", text_lines);//写回txt