add string to memo box line, then empty string, add new input on next line - delphi 2010 - help!

what im trying to do:

input in an edit box, write it to a memo box line on button click, when a 0 or -1 is entered move on to next line of edit box

code:

procedure TForm1.btnReadClick(Sender: TObject);

var
c, i, j : integer;
ch2 : Char;
txt1, txt2 : string;

begin
c := StrToInt(edt2.Text);   //input    
ch2 := Converteer(c);       //input gets converted to Char

if memC.Lines.Count = 0 then  //start value when memo box empty
begin
    i := 0;
    j := 0;
    txt1 :='';
    txt2 :='';
end;

if c = 0 then         //text naar memo       
begin
i := i + 1;                   // next line ?!?        these two seem not to work        
txt1 := '';                   // empty string ?!?     these two seem not to work         
txt2 := memT.Lines[j] + ch2;    
end

else if c = -1 then   //same, it appears 'i' is maybe reset everytime button is pressed

begin
    i := i + 1;
    j := j + 1;
    txt1 := '';
    txt2 := '';
   end

else if c >= 0 then   // a t/m z

begin
 txt1 := memC.Lines[i] + IntToStr(c);        
 txt2 := memT.Lines[j] + ch2;
end;


memC.Lines[i] := txt1;         //write string to line  , [i] should specify the wich line    
memT.Lines[j] := txt2;         // same

end.

i cant find where/how it goes wrong, it be awesome if someone 开发者_高级运维could give me a hand.

greetz peter

The variables i, j, txt1, txt2 are uninitialised if the memo box memC is not empty. You set them to 0/empty if it is - what are you expecting them to be in other cases? Note that their values won't be preserved across multiple button clicks, because you've declared them as local to this function...