Строка: Строку разбить на слова и слова запихнуть в массив char.

// ff.cpp : Defines the entry point for the console application.
//
 
#include "stdafx.h"
#include<iostream>
#include <stdio.h>
#include <string>
using namespace std;
void main ()
{
  char str[] ="- This, a sample string.";
  char * pch;
  char * mChar;
  int count(0);
  printf ("Splitting string \"%s\" into tokens:\n",str);
  pch = strtok (str," ,.-");
  while (pch != NULL)
  {
    count ++;
    pch = strtok (NULL, " ,.-");
  }
    
  mChar = new char[count];
  int it(0);
  while (pch != NULL)
  {
      //printf ("%s\n",pch);
    mChar[it]=*pch;
    pch = strtok (NULL, " ,.-");
    it ++;
  }
 
  for (int i =0 ;i<count;i++)
      cout<<mChar[i]<<" ";
 
 
system("pause>>void");
}

mChar = new char[count];

#include <iostream>
#include <conio.h>
#include <stdio.h>
#include <string>
using namespace std;
void main()
{
    
    const int SIZE = 100;
    char *ch = new char[SIZE];
    string what;
    //char* to;
    cout << "Write sentence: ";
    gets(ch);
    cout <<"Write word to change: ";
    cin>>what;
    //cout <<"Change to: ";
    //cin>>to;
    char *x[SIZE] = {0};
    char *p = strtok(ch, " ,.-");
    int i = 0;
 
    while(p)
    {
        x[i++] = p;
        p = strtok(NULL, " ,.-");
    }
 
    i = 0;
    cout << endl << endl << "Massiv sostoit iz: ";
    while(x[i] != 0)
    {   
        if (x[i++]==what) {x[i++]="to";}
        
        cout << x[i++] << " ";  
    }
 
   getch();
}