I want to modify this Radix sort C++ to work with strings only. I want to sort words not numbers. I don't know what to change or where to change it. Any suggestions?

// CS 9F 
// March 3, 2012

    // Include files
    #include <iostream>    // used for cin, cout
    #include <conio.h>
    #include <fstream>     // file input/output
    #include <queue>       // class for queue's
    #include <string>      // used for string's
    using namespace std;
    
    // Global Type Declarations
    typedef queue<string> Q;
    
    // Function Prototypes
    void instruct(void);
    void pause ();
    
    int main()
    {	
        // Declaration section
        Q holder, tempholder, sorter[10];
        const char  Digits = 10;            // Number of digits per item
        char numInput[Digits];            // Stores data input
        int bin;                          // Stores digits of queue
        int run1;                         // Records runs for print
        int run2;                         // Records runs for print
    
        // Executable section
    	instruct ();
    
    	cout << "Inserting Data In The Queue\n" ;
    	cout << "----------------------------\n" << endl;
    
        ifstream inDataFile( "radixdata.txt", ios::in); //Open Data File
         if ( !inDataFile )
    	{
    	cerr << "File could not be opened\n";
    	exit(1);
    	}
    		
    	inDataFile >> numInput;	          //Read In Data
    	while ( !inDataFile.eof())        //Stop When End Of File Reached
    	      {
    	      holder.push(numInput);      //Put Data In Queue
                  inDataFile >> numInput;     //Read In Next Line Of Data
    	      }
    
    		run1 = 0;
    		tempholder = holder;                 //Copy holder queue to tempholder
    		cout << "Data In The Queue\n\n";
            while (!tempholder.empty())
    	      {					     //Print Out Unsorted Queue
    	      cout << tempholder.front() << " ";
    	      tempholder.pop();
                  run1++;
    
    		if ( run1 % 10 == 0 )
    		    cout <<endl;
    	      }
    
    		cout << "\n\nBeginning Sort Of The Queue" << endl;
    		cout << "----------------------------" << endl;
    		pause();
    
        for ( int i = Digits - 1; i > - 1; i-- ) //Begin Sort Of Queue Using Sorter
    	{
            while (!holder.empty())
    	      {
    	      bin = (static_cast<char>(holder.front().at(i))) - 48;
    	      sorter[bin].push(holder.front());
                  holder.pop();
    	      }
        for ( int j = 0; j <= 9; j++ )
    	{
    	while (!sorter[j].empty())           //Run Through Sorter
    	      {
    	       holder.push(sorter[j].front());//Push Front Digit From Holder
                   sorter[j].pop();}              //Pop Out From Sorter   
    	      }
    	}
          
    	       run2 = 0;
    	       cout << "Data In The Sorted Queue\n\n";              
    	       while (!holder.empty())
    		     {			         //Print Out Sorted Queue
    		      cout << holder.front() << " ";
    		      holder.pop();
                          run2++;
    
    		if ( run2 % 10 == 0 )
    			cout <<endl;
    		     }
    
        pause();
        return 0;
    }
    void instruct (void)
    {
    	  // Declaration section
    
    	  // Executable section
            cout << "\t************************************************************"<< endl;
    	cout << "\t* This program will read an input file named radixdata.txt,*"<< endl;
    	cout << "\t* which contains a list of words  *"<< endl;
    	cout << "\t* The computer will use this input and perform a    *"<< endl;
    	cout << "\t* radix sort of the words using the queue class. The     *"<< endl;
    	cout << "\t* results of the sort will then be printed to the screen.  *"<< endl;                                 
    	cout << "\t************************************************************"<< endl;
    	cout << endl;
    }
    void pause ()
    {
        // Declaration section
    
        // Executable section
        cout << "\nPress any key to continue...";
        getch();
        cout << "\r";
        cout << "                            ";
        cout << "\r";
    }