add ascii bytes 2

[MerryMadDad]

Hello all, can anyone help me to add a series of ascii numbers together ?

The data comes in two bytes 00 (two seperate bytes) and could be for example 23 the first time and 65 the next time. I want to subract 23 from 65 when the characters are ascii - how ?

any help much appreciated

Robert

 

[towerbase]

The usual way to convert ASCII strings to integers is to call StrToInt or StrToIntDef.

I suggest you use StrToIntDef if there is any chance that the strings may not contain valid ASCII digits.

So to add FieldA to FieldB your code might look something like:

function AddFields ( const FieldA, FieldB: string ): integer;
const
  Invalid = 99999;
var
  a: integer;
  b: integer
begin
  a := StrToIntDef ( FieldA, Invalid );
  b := StrToIntDef ( FieldB, Invalid );
  if ( a <> Invalid ) and ( b <> Invalid ) then
    result := a + be
  else
    raise an error;
end;

There is a little "gotcha" in that StrToInt and StrToIntDef will also convert hexadecimal numbers. I had some invalid decimal data which consisted of 'X16' and StrToIntDef converted this to 22 (decimal) and did not give me an invalid number which was what I was expecting. So take care.

Of course, you should really implement a class called TASCIInumbers or something and define a whole series of methods to do arithmetic but I guess you might consider this overkill.

Andrew

 

[bbegley]

Once you have ascii characters you can do something like this ( I haven't compiled this, but I think it's right. That's the danger of typing in this editor when you lazily depend upon the compiler to fix your mistakes).

Sadly, I have never dealt with data as bytes, so I may be overlooking an important detail (or 5 of them).

function AsciiCharToInt(AChar:Char):integer;
begin
if ((ord(AChar) >= 48) and (ord(AChar) <= 57)) then
AsciiInteger = ord(AChar);
end;

You can add the characters together as strings like this

i := StrToInt(IntToStr(AsciiCharToInt(Char1)) + IntToStr(AsciiCharToInt(Char2)));

or like this

i := (AsciiCharToInt(Char1)*10) + AsciiCharToInt(Char2)

Brian &quot;The difference between practice and theory is that in theory, there is no difference between practice and theory&quot; - Somebody's tag line I stole

 

[bbegley]

I didn't know about that StrToIntDef function. I only wish I'd known sooner. Star for you. &quot;The difference between practice and theory is that in theory, there is no difference between practice and theory&quot; - Somebody's tag line I stole

 

[MerryMadDad]

Thanks to Andrew and Brian for their posts, but I still have a problem with this. I thought of strtoint and that stuff, but the problem I have is that each character or number is a seperate byte, so what do I do to detect a &quot;carry&quot; as in 9 + 9 would give 18 but the 8 should be in the &quot;low&quot; byte and the &quot;1&quot; added to the contents of the next byte. I guess subtraction would be similar

Regards Robert

 

[LorenPechtel]

So, strip off the extra digit and do the carry yourself, the same as if you were doing it pencil and paper.

 

[Zathras]

It is not clear to me what you are asking for. On one hand you refer to &quot;add ascii bytes&quot; and in the request you refer to &quot;subtract 23 from 65&quot;

If you mean that you are getting a &quot;number&quot; like 65 as two bytes (strings) &quot;6&quot; and &quot;5&quot; and another &quot;number&quot; like 18 as two bytes (strings) &quot;1&quot; and &quot;8&quot; then this may be the function you are looking for. If not, please explain more carefully what it is that you really need.

function AddBytes( var B1High, B1Low:string; B2High, B2Low:string ):boolean;
var
  B1,B2:integer;
begin
  Result := False;
  B1 := StrToIntDef(B1High+B1Low,-1);
  B2 := StrToIntDef(B2High+B2Low,-1);
  if B1 >= 0 then
    if B2 >= 0 then
      begin
        B1 := B1 + B2;
        if B1 < 99 then
          begin
            B1High := Copy(IntToStr(B1),1,1);
            B1Low  := Copy(IntToStr(B1),2,1);
            Result := True;
          end;
      end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  B1H,B1L:string;
begin
  B1H := '1';
  B1L := '8';
  if AddBytes( B1H, B1L, '6', '5' ) then
    ShowMessage('Answer=' + B1H + B1L )
  else
    ShowMessage('Error');
end;

 

[MerryMadDad]

Thank you Zathras, the first procedure seems to be what I am looking for the numbers or characters come in as seperate bytesand it is these that I want to add or subtract sorry for the confusion - I'm old

Loren, I don't know how to &quot;strip off&quot; the extra digit, I'll go away now and try Zathras suggestin

Thanks to all

Robert

 

[MerryMadDad]

Thank you Zathras, the first procedure seems to be what I am looking for the numbers or characters come in as seperate bytesand it is these that I want to add or subtract sorry for the confusion - I'm old

Loren, I don't know how to &quot;strip off&quot; the extra digit, I'll go away now and try Zathras suggestion

Thanks to all

Robert

 

[Zathras]

Thank you.

If you use the code, please correct the line

if B1 < 99 then

which should have been

if B1 <= 99 then

(I'm old, too. )

 

[MerryMadDad]

Hello Zathras, your suggestion worked fine thank you, I modified it to cater for more than two bytes and to cope with a carry in the case where the answer is <99 but now could you help me do the same but for subtraction ?

much appreciated

Robert - no good at maths

 

[Zathras]

You don't give one a lot to work with, but here goes:

Directions for subtraction:

Use the &quot;-&quot; symbol in place of the &quot;+&quot; symbol.

 

[MerryMadDad]

Thank you Zathras
but what happens when the low byte is larger than the High byte during the use of the &quot;-&quot; sign ?

I mean that I am getting a &quot;number&quot; like 18 as two bytes (strings) &quot;1&quot; and &quot;8&quot; and another &quot;number&quot; like 65 as two bytes (strings) &quot;6&quot; and &quot;5&quot; and I want to subtract these two 18 - 65 could you help out again please ?

Thanks

Robert

 

[Zathras]

First you asked for a routine to handle &quot;two bytes&quot; but then you said you &quot;modified it to cater for more than two bytes.&quot; It is still not clear to me what you really want.

Here are functions to handle up to four bytes, but without really knowing how the data is coming to you I don't know whether this is what you really want. For example, when set up for 4 bytes, and one of the numbers is &quot;65&quot; is the first byte &quot;6&quot; and the second &quot;5&quot; and the third and fourth blank, or is the first one &quot;0&quot;, the second one &quot;0&quot;, the third one &quot;6&quot; and the fourth one &quot;5&quot;? Or is there some other configuration that you have in mind? Are you trying to set up a high-precision math routine that could take more than 255 digits? I can't help you any more without specific requirements.

{Service function called by AddBytes and SubBytes}
function AddOrSubBytes( var Operand1:string; Operand2:string;
             var Negative:boolean; Subtract:boolean=False ):boolean;
var
  Op1,Op2:integer;
begin
  Op1 := StrToIntDef(Operand1,-1);
  Op2 := StrToIntDef(Operand2,-1);
  if (Op1 >= 0) and (Op2 >= 0) then
    begin
      if Subtract then
        Op1 := Op1 - Op2
      else
        Op1 := Op1 + Op2;
      if Op1 < 0 then
        begin
          Negative := True;
          Op1 := 0 - Op1;
        end;
      Operand1 := IntToStr(Op1);
      if Length(Operand1) < Length(Operand2) then
        Operand1 := StringOfChar(' ',Length(Operand2)-Length(Operand1)) + Operand1;
      Result := True;
    end
  else
    Result := False;
end;

{Add two &quot;numbers&quot; together (formatted as strings)}
function AddBytes( var Operand1:string; Operand2:string ):boolean;
var
  Negative:boolean;
begin
  Result := AddOrSubBytes( Operand1, Operand2, Negative);
end;

{Subtract two &quot;numbers&quot; (formatted as strings)}
function SubBytes( var Operand1:string; Operand2:string; var Negative:boolean ):boolean;
begin
  Result := AddOrSubBytes( Operand1, Operand2, Negative, True);
end;

{Demo use of AddBytes function}
procedure DemoAddBytes( Byte1A,Byte2A,Byte3A,Byte4A,
                        Byte1B,Byte2B,Byte3B,Byte4B:string);
var
  X1,X2:string;
begin
  X1 := Byte1A + Byte2A + Byte3A + Byte4A;
  X2 := Byte1B + Byte2B + Byte3B + Byte4B;
  if AddBytes( X1, X2 ) then
    ShowMessage('Answer=' + X1 )
  else
    ShowMessage('Error');
end;

{Demo use of SubBytes function}
procedure DemoSubBytes( Byte1A,Byte2A,Byte3A,Byte4A,
                        Byte1B,Byte2B,Byte3B,Byte4B:string);
var
  X1,X2:string;
  s:string;
  Neg:boolean;
begin
  X1 := Byte1A + Byte2A + Byte3A + Byte4A;
  X2 := Byte1B + Byte2B + Byte3B + Byte4B;
  if SubBytes( X1, X2, Neg ) then
    begin
      if Neg then s := 'minus ' else s := 'plus ';
      ShowMessage('Answer=' + s + X1 )
    end
  else
    ShowMessage('Error');
end;

{Get text from edit boxes and split into 8 bytes to demo AddBytes}
procedure TForm1.Button3Click(Sender: TObject);
var
  Text1,Text2:string;
  Byte1A,Byte2A,Byte3A,Byte4A:string;
  Byte1B,Byte2B,Byte3B,Byte4B:string;
begin
  Text1 := Copy('0000' + Edit3.Text,Length(Edit3.Text)+1,4);
  Text2 := Copy('0000' + Edit4.Text,Length(Edit4.Text)+1,4);
  Byte1A := Copy(Text1,1,1);
  Byte2A := Copy(Text1,2,1);
  Byte3A := Copy(Text1,3,1);
  Byte4A := Copy(Text1,4,1);
  Byte1B := Copy(Text2,1,1);
  Byte2B := Copy(Text2,2,1);
  Byte3B := Copy(Text2,3,1);
  Byte4B := Copy(Text2,4,1);
  DemoAddBytes( Byte1A,Byte2A,Byte3A,Byte4A,
                        Byte1B,Byte2B,Byte3B,Byte4B);
end;

{Get text from edit boxes and split into 8 bytes to demo SubBytes}
procedure TForm1.Button4Click(Sender: TObject);
var
  Text1,Text2:string;
  Byte1A,Byte2A,Byte3A,Byte4A:string;
  Byte1B,Byte2B,Byte3B,Byte4B:string;
begin
  Text1 := Copy('0000' + Edit3.Text,Length(Edit3.Text)+1,4);
  Text2 := Copy('0000' + Edit4.Text,Length(Edit4.Text)+1,4);
  Byte1A := Copy(Text1,1,1);
  Byte2A := Copy(Text1,2,1);
  Byte3A := Copy(Text1,3,1);
  Byte4A := Copy(Text1,4,1);
  Byte1B := Copy(Text2,1,1);
  Byte2B := Copy(Text2,2,1);
  Byte3B := Copy(Text2,3,1);
  Byte4B := Copy(Text2,4,1);
  DemoSubBytes( Byte1A,Byte2A,Byte3A,Byte4A,
                        Byte1B,Byte2B,Byte3B,Byte4B);
end;

 

[MerryMadDad]

Hi Zathras, Thank you very much for the help, you are very kind. What I really wanted was to add or subtract a six byte number where the bytes are presented as ascii characters, perhaps I should have said that at the start, but I thought if I got the basics, I could take it from there. You have helped a great deal and now the case is closed for me

Sorry for any confussion again, put it down to one of the following:

1 I hadn't had my warm glass of milk
2 It was the cat - it distracted me
3 The bairn was screaming his heed off
4 I was sober
5 old age ?

You choose !

Thanks again and best regards

 

[sggaunt]

If you have a screaming bairn, you cant be that old?
Steve

 

[MerryMadDad]

Final comment on this forum as the following has not a lot to do with Delphi Pascal or any other prog. language.
RE screaming bairn if anyone is interested in finding out more contact me on alnet@lineone.net

(Old) Robert