一个新算法的表达式求值的函数

作者： e271828

我经过思考，自已做了一个表达式求值的函数，与标准算法不同，这是我闭门造车而成的，目的在于求简单。我这个函数有两个BUG，我目前已懒得改，当然是可以改的，一个是小数点0.999999999。。。。。未自动消除为1，二是本来乘法与除法是同级的，我这是成了乘法高级过除法。时间匆忙，来不及多说，让读者看了再说吧。另辟溪径也许有利于开拓新思路吧。我的邮箱是

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls,StrUtils, Spin;

type
TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Button1: TButton;
    Button2: TButton;
    SpinEdit1: TSpinEdit;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
private
    { Private declarations }
public
    { Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}
function   nospace(s:string):string;
begin
result:= stringreplace(s,´ ´,´´,[rfReplaceAll]);
end;
function   is123(c:char):boolean;
begin
if c in [´0´..´9´,´.´]
then result:=true
else   result:=false;

end;
function isminus(s:string;i:integer):boolean ;
var
t:integer;
begin

for t:=i-1 downto 1 do
begin
   if s[t]=´)´ then
   begin
   result:=false;
   break;
   end;
   if (s[t]=´(´) and (s[t+1]=´-´) then
   begin
    result:=true;
    break;
   end;
   if (not is123(s[t])) and ( not ((s[t]=´-´) and(s[t-1]=´(´))) then
   begin
   result:=false;
   break;
   end;
end;
end;

function firstJ(s:string):integer ;
var
i,L:integer;
begin
result:=0;
L:=length(s);
for i:=1 to L do
begin
   if (s[i]=´)´) and (not isminus(s,i)) then
   begin
   result:=i;
   break;
   end;

end;
end;
function firstC(s:string;firstJ:integer):integer ;
var
t:integer;
begin
for t:=firstJ downto 1 do
begin
   if (s[t]=´(´) and (s[t+1]<>´-´) then
   begin
    result:=t;
    break;
   end;

end;
end;
function firstsign(s:string):integer ;
var
i:integer;
begin
result:=0;
for i:=1 to length(s) do
    if s[i] in [´+´,´-´,´*´,´/´] then
    begin
    result:=i;
    exit;
    end;
end;
function firstsignEX(s:string;sigh:char):integer ;
var
i:integer;
begin
result:=0;
for i:=1 to length(s) do
    if s[i]=sigh then
    begin
    result:=i;
    exit;
    end;
end;
function firstMinussignEX(s:string):integer ;
var
i:integer;
begin
result:=0;
for i:=1 to length(s) do
    if (s[i]=´-´) and (s[i-1]<>´(´) then
    begin
    result:=i;
    exit;
    end;
end;
function secondsign(s:string):integer ;
var
i,j:integer;
begin
j:=firstsign(s);

for i:=j+1 to length(s) do
    if s[i] in [´+´,´-´,´*´,´/´] then
    begin
    result:=i;
    exit;
    end;
result:=length(s);
end;
function secondsignEX(s:string;sigh:char):integer ;
var
i,j:integer;
begin
j:=firstsignex(s,sigh);

for i:=j+1 to length(s) do
    if s[i]   in [´+´,´-´,´*´,´/´] then
    begin
    result:=i;
    exit;
    end;
result:=length(s);
end;
function leftnum(s:string;i:integer):double ;
var
t,L:integer;
begin
L:=length(s);
if s[i-1]=´)´ then
begin
for t:=i-1 downto 1 do
if s[t]=´(´ then
begin
result:=strtofloat(copy(s,t+1,i-2-t));
exit;
end;
end
else
begin
   for t:=i-1 downto 1 do
   begin
     if not is123(s[t]) then
     begin
       result:=strtofloat(copy(s,t+1,i-1-t));
       exit;
     end;
     if t=1 then result:=strtofloat(leftstr(s,i-1));
   end;
end;

end;
function rightnum(s:string;i:integer):double ;
var
t,L:integer;
begin
L:=length(s);
if s[i+1]=´(´ then
begin
for t:=i+2 to L do
if s[t]=´)´ then
begin
result:=strtofloat(copy(s,i+2,t-i-2));
exit;
end;
end
else
begin
   for t:=i+1 to L do
   begin
     if not is123(s[t]) then
     begin
       result:=strtofloat(copy(s,i+1,t-i-1));
       exit;
     end;
     if t=L then result:=strtofloat(rightstr(s,L-i));
   end;
end;
end;
/////////////////////////////////
function leftsigh(s:string;i:integer):integer ;
var
t,L:integer;
begin
L:=length(s);
if s[i-1]=´)´ then
begin
for t:=i-1 downto 1 do
if s[t]=´(´ then
begin
result:=t;
exit;
end;
end
else
begin
   for t:=i-1 downto 1 do
   begin
     if not is123(s[t]) then
     begin
       result:=t+1;
       exit;
     end;
     if t=1 then result:=1;
   end;
end;

end;
function rightsigh(s:string;i:integer):integer ;
var
t,L:integer;
begin
L:=length(s);
if s[i+1]=´(´ then
begin
for t:=i+2 to L do
if s[t]=´)´ then
begin
result:=t;
exit;
end;
end
else
begin
   for t:=i+1 to L do
   begin
     if not is123(s[t]) then
     begin
       result:=t-1;
       exit;
     end;
     if t=L then result:=L;
   end;
end;
end;
////////////////////////////////////

function nomulti(s:string):string ;
var
i,L,le,ri:integer;
j,k:double ;
begin
s:=nospace(s);
result:=s;
L:=length(s);
i:=firstsignex(s,´*´);
if (i=0) or (s[i]<>´*´) then exit;
le:=leftsigh(s,i);
j:=leftnum(s,i);
k:=rightnum(s,i);
ri:=rightsigh(s,i);
ii<L then
if j*k>=0 then
result:=nomulti(leftstr(s,le-1)+floattostr(j*k)+rightstr(s,L-ri))
else
result:=nomulti(leftstr(s,le-1)+´(´+floattostr(j*k)+´)´+rightstr(s,L-ri))

end;
function nodiv(s:string):string ;
var
i,L,le,ri:integer;
j,k:double ;
begin
s:=nospace(s);
result:=s;
L:=length(s);
i:=firstsignex(s,´/´);
if (i=0) or (s[i]<>´/´) then exit;
le:=leftsigh(s,i);
j:=leftnum(s,i);
k:=rightnum(s,i);
ri:=rightsigh(s,i);
if j/k>=0 then
result:=nodiv(leftstr(s,le-1)+floattostr(j/k)+rightstr(s,L-ri))
else
result:=nodiv(leftstr(s,le-1)+´(´+floattostr(j/k)+´)´+rightstr(s,L-ri))

end;
function noadd(s:string):string ;
var
i,L,le,ri:integer;
j,k:double ;
begin
s:=nospace(s);
result:=s;
L:=length(s);
i:=firstsignex(s,´+´);
if (i=0) or (s[i]<>´+´) then exit;
le:=leftsigh(s,i);
j:=leftnum(s,i);
k:=rightnum(s,i);
ri:=rightsigh(s,i);
if j+k>=0 then
result:=noadd(leftstr(s,le-1)+floattostr(j+k)+rightstr(s,L-ri))
else
result:=noadd(leftstr(s,le-1)+´(´+floattostr(j+k)+´)´+rightstr(s,L-ri))

end;
function nosub(s:string):string ;
var
i,L,le,ri:integer;
j,k:double ;
begin
s:=nospace(s);
result:=s;
L:=length(s);
i:=firstMinussignEX(s);
if (i=0) or (s[i]<>´-´) then exit;
le:=leftsigh(s,i);
j:=leftnum(s,i);
k:=rightnum(s,i);
ri:=rightsigh(s,i);
if j-k>=0 then
result:=nosub(leftstr(s,le-1)+floattostr(j-k)+rightstr(s,L-ri))
else
result:=nosub(leftstr(s,le-1)+´(´+floattostr(j-k)+´)´+rightstr(s,L-ri))

end;
function alltoone(s:string):string ;
begin
s:=nomulti(s);
s:=nodiv(s);
s:=noadd(s);
s:=nosub(s);
result:=s;
end;

function myexpress(s:string):string;
var
c,j,L:integer;
le,ri,al,substr,s0:string;
tryit:double;
begin
s:=nospace(s);
s0:=s;
L:=length(s);
if (s[1]<>´(´) or (s[L]<>´)´) then
s:=´(´+s+´)´;
if (s[1]=´(´) and (s[L]=´)´) and((s[2]=´-´) or (isminus(s,L))) then
s:=´(´+s+´)´;
L:=length(s);
j:=firstJ(s);
c:=firstc(s,j);
if (j<L) and (c>1) and (j>c) then
begin
substr:=copy(s,c+1,j-c-1);
(s,c-1);
rightstr(s,L-j);
le:=leftstr(s,c-1);
le:=rightstr(le,length(le)-1);
ri:= rightstr(s,L-j);
ri:=leftstr(ri,length(ri)-1);
(substr);
al:=alltoone(substr);
(le+al+ri);
result:=myexpress(le+al+ri);
end
else
result:=alltoone(s0);

end;
procedure TForm1.Button1Click(Sender: TObject);
begin
Edit2.Text:=myexpress(edit1.text);
end;

end.

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