Question

Passing a string equation to become an integer

Asked by: CrazyOne

ok I have two text boxes. The user enters a equation to be calculated in one of the boxes and the other, after clicking a button, provides the answer. The problem occurs when passing the string to become an integer at the StrToInt(sEquation). Error is "Not a valid integer"

for example this equation (975 - 369) x (943 x 384 + 100)



procedure TForm1.Button1Click(Sender: TObject);
var
  iEquation: Integer;
  sEquation: String;

begin

  sEquation := edtEquation.Text;
  {changes character x to * to satisfy the compilers need to recognize the symbol used to multiply with}
  while Pos('x', sEquation) > 0 do
    sEquation[Pos('x', sEquation)] := '*';
  edtEquation.Text :=  sEquation;
  {error happens on the following line}
  iEquation := StrToInt(sEquation);
  edtAnswer.Text := IntToStr(iEquation);
  edtAnswer.SetFocus;

end;

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Asked On
2009-02-16 at 15:03:37ID24148380
Topic

Delphi Programming

Participating Experts
2
Points
500
Comments
9

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Answers

 

by: rfwoolfPosted on 2009-02-16 at 15:14:47ID: 23654863

I guess intead of using an integer (which won't allow decimals) use a double or float. (strtofloat etc)

 

by: CrazyOnePosted on 2009-02-16 at 15:16:41ID: 23654876

I did it doesnt matter what type i use the error still occurs

 

by: SteveBayPosted on 2009-02-16 at 15:17:46ID: 23654891

Changing : '(975 - 369) x (943 x 384 + 100)'
to: '(975 - 369) * (943 * 384 + 100)'
does not make it an expression that can be recognized as an integer.
To find the solution to this equation you will need parse for all numbers and operators separately and build the expression in code.

 

by: SteveBayPosted on 2009-02-16 at 15:21:49ID: 23654929

for example
StrToInt('100') = 100
StrToInt('10 * 10') = Error! not a valid integer.
StrToInt('10') * StrToInt('10') = 100

 

by: CrazyOnePosted on 2009-02-16 at 15:22:40ID: 23654944

Yeah I can understand that but when i do something like the following it works so why the difference

   iEquation := (975 - 369) * (943 * 384 + 100);

  {and then}

  edtAnswer.Text := IntToStr(iEquation);
  edtAnswer.SetFocus;

 

by: CrazyOnePosted on 2009-02-16 at 15:23:50ID: 23654955

Oh ok I see what u are driving at. What a pain :>)

 

by: SteveBayPosted on 2009-02-16 at 15:27:32ID: 23654984

There may be a component somewhere out htere that can do what you are trying to do. I've never looked for one.

 

by: SteveBayPosted on 2009-02-16 at 15:29:16ID: 23654999

 

by: CrazyOnePosted on 2009-02-16 at 17:11:41ID: 31547569

That link gives access to code that did the job for me thanks

20120131-EE-VQP-002

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