Pascal/Turbo Pascal - CADENAS STRING MAYÚSCULAS/MINÚSCULAS

{Esto podría valerte la cadena la puedes entrar con readln ejemplo :

 var

     texto : strin78;

     readln(texto);

    inversionletras(texto) }

program inversion;

 uses

    crt;

  type

    strin78 = string[78];

  var

    pul : char;

 procedure  inversionletras(c : strin78);

 var

   cont : integer;

   cat : strin78;

  begin

      cat := copy(c,1,length(c));

      cont := 1;

      clrscr;

     repeat

        if cat[cont] in[#1..#31,#33..#38,#65..#90,#165,#97..#122,#164] then

        begin

          if cat[cont] in[#65..#90,#165] then

          begin

             cat[cont] := char(ord(cat[cont]) + 32);

             cont := cont + 1;

          end;

          if cat[cont] in[#97..#122,#164] then

          begin

             cat[cont] := upcase(cat[cont]);

             cont := cont + 1;

          end;

          if cat[cont] in[#1..#31,#33..#43,#45,#47,#58..#64,#91..#96,

                                      #123..#163,#166..#254] then

          begin

             cat[cont] := '?';

             cont := cont + 1;

          end;

        end

      else

      cont := cont + 1;

      until cont > length(c);

      writeln;

      writeln('***** El Cambios Realizados *****');

      writeln;

      for cont := 1 to length(c) do

      write(c[cont]);

      writeln;

      writeln;

      for cont := 1 to length(c) do

      write(cat[cont]);

      writeln;

      writeln;

      writeln('<<<< Pulse [Enter] >>>>');

      repeat

         pul := readkey;

     until pul = #13;

  end;

  begin

      inversionletras('BUENOS DIAS! a los 120 Alumnos, mas O menos.');

  end.