C#替换字符串中子串

using System;    
using System.Collections.Generic;    
using System.Linq;    
using System.Text;    
    
class Program    
{    
    
    /// <summary>    
    ///     
    /// </summary>    
    /// <param name="str">待处理的字符串</param>    
    /// <param name="toRep">要替换的字符串中的子串</param>    
    /// <param name="strRep">用来替换toRep字符串的字符串</param>    
    /// <returns>返回一个结果字符串</returns>    
    
    public static string StringReplace(string str, string toRep, string strRep)    
    {    
        StringBuilder sb = new StringBuilder();    
    
        int np = 0, n_ptmp = 0;    
    
        for (; ; )    
        {    
            string str_tmp = str.Substring(np);    
            n_ptmp = str_tmp.IndexOf(toRep);    
    
            if (n_ptmp == -1)    
            {    
                sb.Append(str_tmp);    
                break;    

    1.             }    

            else    
            {    
                sb.Append(str_tmp.Substring(0, n_ptmp)).Append(strRep);    
                np += n_ptmp + toRep.Length;    
            }    
        }    
        return sb.ToString();    
    
    }    
    
    
    /// <summary>    
    /// 测试用例:"dwdawdyesdwjdao dyesj yes dwjaodjawiodayes djwaiodyesjijw"    
    /// </summary>    
    /// <param name="args"></param>    
    
    static void Main(string[] args)    
    {    
        string str = Console.ReadLine();    
        str = StringReplace(str, "yes", "no");    
        Console.WriteLine(str);    
        Console.ReadKey();    
    }    
}