Вычисление простых арифметических выражений



Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

function Calculate(SMyExpression: string; digits: Byte): string;
// Calculate a simple expression 
// Supported are:  Real Numbers, parenthesis 
var
z: Char;
ipos: Integer;
function StrToReal(chaine: string): Real;
var
r: Real;
Pos: Integer;
begin
Val(chaine, r, Pos);
if Pos > 0 then Val(Copy(chaine, 1, Pos - 1), r, Pos);
Result := r;
end;
function RealToStr(inreal: Extended; digits: Byte): string;
var
S: string;
begin
Str(inreal: 0: digits, S);
realToStr := S;
end;
procedure NextChar;
var
s: string;
begin
if ipos > Length(SMyExpression) then
begin
z := #9;
Exit;
end
else
begin
s := Copy(SMyExpression, ipos, 1);
z := s[1];
Inc(ipos);
end;
if z = ' ' then nextchar;
end;
function Expression: Real;
var
w: Real;
function Factor: Real;
var
ws: string;
begin
Nextchar;
if z in ['0'..'9'] then
begin
ws := '';
repeat
ws := ws + z;
nextchar
until not (z in ['0'..'9', '.']);
Factor := StrToReal(ws);
end
else if z = '(' then
begin
Factor := Expression;
nextchar
end
else if z = '+' then Factor := +Factor
else if Z = '-' then Factor := -Factor;
end;
function Term: Real;
var
W: Real;
begin
W := Factor;
while Z in ['*', '/'] do
if z = '*' then w := w * Factor
else
w := w / Factor;
Term := w;
end;
begin
w := term;
while z in ['+', '-'] do
if z = '+' then w := w + term
else
w := w - term;
Expression := w;
end;
begin
ipos   := 1;
Result := RealToStr(Expression, digits);
end;
procedure TForm1.Button1Click(Sender: TObject);
var
sMyExpression: string;
begin
sMyExpression := '12.5*6+18/3.2+2*(5-6.23)';
ShowMessage(sMyExpression + ' = ' + Calculate(sMyExpression, 3));
end;

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