方法一

代码如下:

static void Main()
{
     string s = "123456789";
     SwapChar(ref s, 3, 6);
     Console.Write(s.ToString());
}

static void SwapChar(ref string s, int i1, int i2)
{
    char temp = s[i1];
    char temp1 = s[i2];
    s = s.Remove(i1, 1).Insert(i1, temp1.ToString());
    s = s.Remove(i2, 1).Insert(i2, temp.ToString());
}

方法二

代码如下:

static void Main()
...{
       string s = "123456789";
       //SwapChar(s, 3, 6);
       Console.Write(SwapChar(s, 3, 6).ToString());
}

static string SwapChar(string s, int p1, int p2)
...{
        if ((p1 == p2) || ((p1 < 0) || (p2 < 0))) return s;
        if ((p1 >= s.Length) || (p2 >= s.Length)) return s;
        char[] vChars = s.ToCharArray();
        vChars[p1] = (char)(vChars[p2] | (vChars[p2] = vChars[p1]) & 0);
        return new string(vChars);
}

方法三

代码如下:

static void Main()
...{
        string s = "123456789";
        Console.Write(SwapChar(s, 3, 6).ToString());
}

public static string SwapChar(string str, int a, int b)
...{
        char[] newStr = str.ToCharArray();
        newStr[a] = str[b];
        newStr[b] = str[a];
        return new string(newStr);
}

方法四

代码如下:

using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;
namespace ConsoleApplication1
...{
    class Program
    ...{
        static void Main()
        ...{
            string s = "123456789";
            Console.Write(SwapChar(s, 3, 6).ToString());
        }

        static string SwapChar(string s, int p1, int p2)
        ...{
            if (p1 > p2) ...{ int p = p1; p1 = p2; p2 = p; }
            return Regex.Replace(s, "^(.{" + p1 + "})(.)(.{" + (p2 - p1 - 1) + "})(.)(.*)$", "$1$4$3$2$5");
        }
    }
}