Text Line Editor Program
- Very Simple Version

This is a very simple text line editor, it does not even save anything to
a file or allow the deletion of lines.   Nevertheless, the simple command
dispatcher loop structure introduced here means that new functionality,
such as saving data to files, deleting lines, display of the file directory
and string search functions can be added as modules in the command
dispatcher.

Once we introduce functions, we will be able to simplify and shorten
the program while adding functionality, demonstrating the power and
utility of functions.

As we progress emphasis will be on dealing with the human interface;
while this program as it exists here will go out of control when a letter is
entered where a number is expected, these problems will be dealt with
one at a time.

In order to deal with multiple lines of text data, a two dimensional
character array is introduced even though this is not formally covered
until toward the end of the class, enough detail will be covered in class
to deal with this level of complexity.

You can just cut this program and paste it into Visual Studio:

//   File Editor Demonstration Program    -  Simple 
//   Jim Engel  
//   Version     April 5, 2011      

/*   This is a class project intended to demonstrate a 
     primitive line by line text editor, including 
     command dispatcher operation.  This editor is of
     course not a replacement for the many text editors
     in use, primarily because it stores text line by line
     with no provision for fold over.  In principle, it
     could maintain a list style of text file.
       ***************************************************/ 
#include <iostream>
#include <cstring>

using namespace std;

const int LINE_LEN  = 81;    //  length of each text line 
const int LINE_CNT  = 14;    //  max number of lines in edited text

const int CMD_SZ    = 40;    //  size of the command string.


//      MAIN PROGRAM
int main( )
{  int mark;                              //  General purpose counter
   int line;                              //  Line marker
   int count;                             //  used as line counter
   char command[CMD_SZ];                  //  User command text srring
   char  text[LINE_CNT][LINE_LEN];        //  Text lines being manipulated

   for ( mark = 0;  mark < LINE_CNT; ++mark ) {   //  Initialize our main text storage
         text[mark][0] = 0;
   }
   cout << "\nTHE VERY SIMPLE HANDY DANDY TEXT LINE EDITOR.....\n";  

   /*****************            COMMAND DISPATCH LOOP                  ****************/
   while ( true )
   {
      cout << "\nEnter a command: ";
      cin.getline(command, CMD_SZ);
      command[3] = 0;                    // Limit string to 3 char.
      cout << "Command:   "<< command << "\n";

      if     ( !strcmp(command, "end"))                         /***   END Command   ***/
      {   break;
      }

      else if( !strcmp(command, "hel"))                              /***  HELP Command   ***/
      {   cout << "\nCommands are:  \n"
                  "HELP    Display commands\n"
                  "END     Exit from this program\n"
                  "CHANGE  a line of text\n"
                  "LIST    current text lines\n"
                  "\n";
      }

      else if( !strcmp(command, "lis"))                              /*** LIST  Command   ***/
      {  for ( count = 0,mark = 0; mark < LINE_CNT; ++mark) {  //  Find out how many lines,
            if ( text[mark][0] != 0 )                          //  including empty lines.
               count = mark;
         }
         for ( line = 0; line <= count; ++line ) {
             cout << line << ": " << text[line]  << endl;
         }
         cout << "Number of lines:  " << count << endl;
      }

      else if( !strcmp(command, "cha")   )                           /***   CHANGE Command   ***/
      {  cout << "Line to chanage:";
         cin  >> line;
         if ( line < 0 || line >= LINE_CNT ) {
            cout << "Invalid line  " << line << endl<< endl;
            continue;
         }
         cout << "New line text: " ;
         cin.ignore ( );
         cin.getline ( text[line], LINE_LEN );
      }
      else
         cout << "Your command is NOT valid!\n";
   }

   cout << "\nDats all folks.....\n\n";
   return 0;
}