Преобразование строки в математическое выражение и получение результата

unit MathComponent;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls,
  Forms, Dialogs, math;

type
  TMathtype = (mtnil, mtoperator, mtlbracket, mtrbracket, mtoperand);

type
  TMathOperatortype = (monone, moadd, mosub, modiv, momul, mopow);

type
  pmathchar = ^Tmathchar;
  TMathChar = record
  case mathtype: Tmathtype of
    mtoperand:(data:extended);
    mtoperator:(op:TMathOperatortype);
  end;

type
  TMathControl = class(TComponent)
  private
    input, output, stack: array of tmathchar;
    fmathstring: string;
    function getresult:extended;
    function calculate(operand1,operand2,operator:Tmathchar):extended;
    function getoperator(c:char):TMathOperatortype;
    function getoperand(mid:integer;var len:integer):extended;
    procedure processstring;
    procedure convertinfixtopostfix;
    function isdigit(c:char):boolean;
    function isoperator(c:char):boolean;
    function getprecedence(mop:TMathOperatortype):integer;
  protected
  published
    property MathExpression:string read fmathstring write fmathstring;
    property MathResult:extended read getresult;
  end;

procedure register;

implementation

function Tmathcontrol.calculate(operand1,operand2,operator:Tmathchar):extended;
begin
  result:=0;
  case operator.op of
    moadd:
      result:=operand1.data + operand2.data;
    mosub:
      result:=operand1.data - operand2.data;
    momul:
      result:=operand1.data * operand2.data;
    modiv:
      if (operand1.data<>0) and (operand2.data<>0) then
        result:=operand1.data / operand2.data
      else
        result := 0;
    mopow:
      result:=power(operand1.data, operand2.data);
  end;
end;

function Tmathcontrol.getresult:extended;
var
  i:integer;
  tmp1,tmp2,tmp3:tmathchar;
begin
  convertinfixtopostfix;
  setlength(stack,0);
  for i:=0 to length(output)-1 do
  begin
    if output[i].mathtype=mtoperand then
    begin
      setlength(stack,length(stack)+1);
      stack[length(stack)-1]:=output[i];
    end
    else
    if output[i].mathtype=mtoperator then
    begin
      tmp1:=stack[length(stack)-1];
      tmp2:=stack[length(stack)-2];
      setlength(stack,length(stack)-2);
      tmp3.mathtype:=mtoperand;
      tmp3.data:=calculate(tmp2,tmp1,output[i]);
      setlength(stack,length(stack)+1);
      stack[length(stack)-1]:=tmp3;
    end;
  end;
  result:=stack[0].data;
  setlength(stack,0);
  setlength(input,0);
  setlength(output,0);
end;

function Tmathcontrol.getoperator(c:char):TMathOperatortype;
begin
  result:=monone;
  if c='+' then
    result:=moadd
  else
  if c='*' then
    result:=momul
  else
  if c='/' then
    result:=modiv
  else
  if c='-' then
    result:=mosub
  else
  if c='^' then
    result:=mopow;
end;

function Tmathcontrol.getoperand(mid:integer;var len:integer):extended;
var
  i,j:integer;
  tmpnum:string;
begin
  j:=1;
  for i:=mid to length(fmathstring)-1 do
  begin
    if isdigit(fmathstring[i]) then
    begin
      if j<=20 then
        tmpnum:=tmpnum+fmathstring[i];
      j:=j+1;
    end
    else
      break;
  end;
  result:=strtofloat(tmpnum);
  len:=length(tmpnum);
end;

procedure Tmathcontrol.processstring;
var
  i:integer;
  numlen:integer;
begin
  i:=0;
  numlen:=0;
  setlength(output,0);
  setlength(input,0);
  setlength(stack,0);
  fmathstring:='('+fmathstring+')';
  setlength(input,length(fmathstring));
  while i<=length(fmathstring)-1 do
  begin
    if fmathstring[i+1]='(' then
    begin
      input[i].mathtype:=mtlbracket;
      i:=i+1;
    end
    else
    if fmathstring[i+1]=')' then
    begin
      input[i].mathtype:=mtrbracket;
      i:=i+1;
    end
    else
    if isoperator(fmathstring[i+1]) then
    begin
      input[i].mathtype:=mtoperator;
      input[i].op:=getoperator(fmathstring[i+1]);
      i:=i+1;
    end
    else
    if isdigit(fmathstring[i+1]) then
    begin
      input[i].mathtype:=mtoperand;
      input[i].data:=getoperand(i+1,numlen);
      i:=i+numlen;
    end;
  end;
end;


function Tmathcontrol.isoperator(c:char):boolean;
begin
  result:=false;
  if (c='+') or (c='-') or (c='*') or (c='/') or (c='^') then
    result:=true;
end;

function Tmathcontrol.isdigit(c:char):boolean;
begin
  result:=false;
  if ((integer(c)> 47) and (integer(c)< 58)) or (c='.') then
    result:=true;
end;

function Tmathcontrol.getprecedence(mop:TMathOperatortype):integer;
begin
  result:=-1;
  case mop of
    moadd: result := 1;
    mosub: result := 1;
    momul: result := 2;
    modiv: result := 2;
    mopow: result := 3;
  end;
end;

procedure Tmathcontrol.convertinfixtopostfix;
var
  i,j,prec:integer;
begin
  processstring;
  for i:=0 to length(input)-1 do
  begin
    if input[i].mathtype=mtoperand then
    begin
      setlength(output,length(output)+1);
      output[length(output)-1]:=input[i];
    end
    else
    if input[i].mathtype=mtlbracket then
    begin
      setlength(stack,length(stack)+1);
      stack[length(stack)-1]:=input[i];
    end
    else
    if input[i].mathtype=mtoperator then
    begin
      prec:=getprecedence(input[i].op);
      j:=length(stack)-1;
      if j>=0 then
      begin
        while(getprecedence(stack[j].op)>=prec) and (j>=0) do
        begin
          setlength(output,length(output)+1);
          output[length(output)-1]:=stack[j];
          setlength(stack,length(stack)-1);
          j:=j-1;
        end;
        setlength(stack,length(stack)+1);
        stack[length(stack)-1]:=input[i];
      end;
    end
    else
    if input[i].mathtype=mtrbracket then
    begin
      j:=length(stack)-1;
      if j>=0 then
      begin
        while(stack[j].mathtype<>mtlbracket) and (j>=0) do
        begin
          setlength(output,length(output)+1);
          output[length(output)-1]:=stack[j];
          setlength(stack,length(stack)-1);
          j:=j-1;
        end;
        if j>=0 then
          setlength(stack,length(stack)-1);
      end;
    end;
  end;
end;

procedure register;
begin
  RegisterComponents('Samples', [TMathControl]);
end; 

end.