Dll Injection

[James Parsons]

I have found plenty of info on Google, but I am finding it very complex. Can I use it to change the functionality of functions in another program. If so here is my case:

program Test;

procedure Hello;
begin
  WriteLn('Hello, World!');
  ReadLn;
end;

begin
  Hello;
end.                                   

This is the pascal code. I want to use c to change the Hello procedure to say "Goodbye, World!" instead. If it is possible what are the each and every steps I should take in order to get this done