Merry Christmas!
I hope some of the following makes sense - I've not been programming long, and I'm totally self-taught, so I might be making some idiotic mistakes. Here goes...
I am trying to make an ecosystem with 5 or 6 different classes of organism. I've made this one, which works (more or less) with 3 different classes in it.

http://www.scanraid.com/speakingincolour/threeOrgIndex.html

So far so good.
I'm not happy with the way my code is structured at the moment as I think I may run into problems as the system grows. The basic problem is writing reuseable methods for all the classes.
All  classes use more or less the same methods, so to start with I structured the code something like this:

class Org{
 Org(){
   //bla bla
 }
 void birth(){
   //bla bla
 }
 void die(){
// bla bla
 }
 void hunt(){
 //bla bla
 }

 //etc....then:

 class Plant extends Org{
 int itsClass;
   Plant(){
     itsClass = 1;
     //bla bla
     }
 }


 class Prey extends Org{
 int itsClass;
   Prey(){
     itsClass = 1;
     //bla bla
   }
 }

//etc....

}
//------------------------------------------------------------------------------
-

I gave each extended class a variable (int) so it knew whether it was a plant, prey etc. and called the same methods for all organisms. The problem with this was that I couldn't work out a way of putting together the name of an object as a variable value -  eg for the birth method I wrote something like

void birth(){
 string objString;
 int itsMax;
 class thisClass;

 switch(itsClass){
   case 1:
     //maxPlant is the length of the array holding all the plant names
     itsMax = maxPlant;
     objString = "plant";
     //not sure I can do next line
     thisClass = Plant();
     break;
   
    case 2:
     itsMax = maxPrey;
     objString = "prey";
     thisClass = Prey();
     break;

 //etc...
 }

 for(int i =0; i<(itsMax-1); i++){

//then here is where I ran into real difficulties. I need to concatenate objString ("plant", "prey" etc.) with the value of  i to create the name of a new object. Something like:

   if(classString[i]== null);{
     classString[i] == new thisClass;
     break;
   }
 }
}

//------------------------------------------------------------------------------
--

There doesn't seem to be a method for turning strings into useable variables. Also, I can't work out how to refer to the name of a class rather than a specific instance ( I'm sure class thisClass = Plant(); can't be right!). I ended up with pretty much the entire method written out repeatedly for each case and there didn't seem to be much point to having global methods at all, so I got rid of class Org and had all the classes functioning independently with local methods, which is how the program is now.

If I use almost identical local methods throughout will it slow up the program?
Is there a way to solve the problems so that I can use extended classes?

I'd be very grateful for any help on this, and also for any general comments or suggestions.
(by the way, I'm using P3D because I can't get OPENGL to work on my stupid graphics card)

thanks