inlocuire in txt c1 cu c2

#include <iostream>
#include<cstring>
#include<stdio.h>
using namespace std;

int main()
{ char s[256],c1[20],c2[20],sep[]=" .,",*p;
  aux[256];
  gets(s);
  gets(c1);
  gets(c2);
  p=strtok(s,sep);
   while(p)
   {
       if(strcmp(p,c1)==0)
       {
           strcpy(aux,p);
           strcpy(p,c2);
           strcpy(c2,aux);
       }
       cout<<p<<" ";
       p=strtok(NULL,sep);
   }
    return 0;
}