change poisition of two word in a string

string manipulated is very common task in daily programm. you can creat a million of quesiton about string if you want. here i post a string question : change position of two words in a string.
here is my code ....i use in C#. that's my interview question.

using System;
using System.Collections.Generic;
using System.Text;

namespace ReverseString
{
    class ReverseStringAdjactionWord
    {
        //reverses text in between two integer;
        private static void Swap(char[] charArray,int p1, int p2)
        {
            while (p1 < p2)
            {
                char temp;
               
                //swap
                temp = charArray[p1];
                charArray[p1] = charArray[p2];
                p1++;
                charArray[p2] = temp;
                p2--;
            }
        }
        //
        // reverses the complete string
        public static void ReverseString(char[] s)
        {
            //1.basic empty
            if (s == null) return;

            //2. find two word
            if (s.Length > 0)
            {
                //c1 and c2 will point to the first word, and c3 and c4 will point to the second word
                int c1, c2, c3, c4, c5, c6,c7;
                c1 = c2 = c3 = c4 = 0;
               
                //below code will find two word and reverse them....show
                while (c4 < s.Length)
                {
                    //find the first word--------------------------
                    for (; c1 < s.Length && s[c1] == ' '; c1++, c2++) ;//handle multiple spaces between words
                    if (c1 >= s.Length) break;
                    for (; c2 < s.Length && s[c2] != ' '; c2++) ;
                   
                    //find the second word
                    c3 = c4 = c2;
                    for (;  c3 < s.Length && s[c3] == ' '; c3++, c4++) ;//handle multiple spaces between words
                    if (c3 >= s.Length) break;
                    for (; c4 < s.Length && s[c4] != ' '; c4++) ;
                   
                    //reverse the string from c1 to c4-1
                    c5 = c6 = c1;
                    c7 = c4-1;
                    Swap(s, c1, c7);
                    //---------------------------- these code reverse two word
                   
                    //next, reverse word by word
                    while (c6 <= c7)
                    {
                        //handle multiple spaces between words
                        for (; c5 <= c7 && s[c5] == ' '; c5++, c6++) ;
                        if (c5 > c7) break;

                        // find word boundary
                        for (; c6 <= c7 && s[c6] != ' '; c6++) ;

                        Swap(s, c5, c6 - 1);
                       
                        c5 = c6;
                      
                    }
                    c1 = c2 = c3 = c4;
                   
                }

           
            }
        }
    }
}