Matrix in Pascal

matric.pas

program SLM;
 uses crt;
 var a:byte;
function exkey:boolean;
begin
 if keypressed then
  if (ord(readkey)=13) then exkey:=true
  else exkey:=false
 else exkey:=false;
end;

begin
 textbackground(black);
 textcolor(lightgreen);
 clrscr;
 randomize;
 repeat
  a:=random(255);
  if (a=13) or (a=10) then a:=5;
  write(chr(a));
 until exkey;
end.