Contributor: SWAG SUPPORT TEAM
{ Author: Gavin Peters. }
Program PostFixConvert;
(*
* This Program will convert a user entered expression to postfix, and
* evaluate it simultaniously. Written by Gavin Peters, based slightly
* on a stack example given in Algorithms (Pascal edition), pg
*
*)
Var
Stack : Array[1 .. 3] of Array[0 .. 500] of LongInt;
Procedure Push(which : Integer; p : LongInt);
begin
Stack[which,0] := Stack[which,0]+1;
Stack[which,Stack[which,0]] := p
end;
Function Pop(which : Integer) : LongInt;
begin
Pop := Stack[which,Stack[which,0]];
Stack[which,0] := Stack[which,0]-1
end;
Var
c : Char;
x,t,
bedmas : LongInt;
numbers : Boolean;
Procedure Evaluate( ch : Char );
Function Power( exponent, base : LongInt ) : LongInt;
begin
if Exponent> 0 then
Power := Base*Power(exponent-1, base)
ELSE
Power := 1
end;
begin
Write(ch);
if Numbers and not (ch = ' ') then
x := x * 10 + (Ord(c) - Ord('0'))
ELSE
begin
Case ch OF
'*' : x := pop(2)*pop(2);
'+' : x := pop(2)+pop(2);
'-' : x := pop(2)-pop(2);
'/' : x := pop(2) div pop(2);
'%' : x := pop(2) MOD pop(2);
'^' : x := Power(pop(2),pop(2));
'L' : x := pop(2) SHL pop(2);
'R' : x := pop(2) SHR pop(2);
'|' : x := pop(2) or pop(2);
'&' : x := pop(2) and pop(2);
'$' : x := pop(2) xor pop(2);
'=' : if pop(2) = pop(2) then
x := 1
else
x := 0;
'>' : if pop(2)> pop(2) then
x := 1
else
x := 0;
'<' : if pop(2) < pop(2) then x := 1 else x := 0; '0','1'..'9' : begin Numbers := True; x := Ord(c) - Ord('0'); Exit end; ' ' : if not Numbers then Exit; end; Numbers := False; Push(2,x); end; end; begin Writeln('Gavin''s calculator, version 1.00'); Writeln; For x := 1 to 3 DO Stack[x, 0] := 0; x := 0; numbers := False; Bedmas := 50; Writeln('Enter an expression in infix:'); Repeat Read(c); Case c OF ')' : begin Bedmas := Pop(3); Evaluate(' '); Evaluate(Chr(pop(1))); end; '^','%','+','-','*','/','L','R','|','&','$','=','<','>' :
begin
t := bedmas;
Case c Of
'>','<' : bedmas := 3; '|','$', '+','-' : bedmas := 2; '%','L','R','&', '*','/' : bedmas := 1; '^' : bedmas := 0; end; if t <= bedmas then begin Evaluate(' '); Evaluate(Chr(pop(1))); end; Push(1,ord(c)); Evaluate(' '); end; '(' : begin Push(3,bedmas); bedmas := 50; end; '0','1'..'9' : Evaluate(c); end; Until Eoln; While Stack[1,0] 0 DO
begin
Evaluate(' ');
Evaluate(Chr(pop(1)));
end;
Evaluate(' ');
Writeln;
Writeln;
Writeln('The result is ',Pop(2));
end.
{
That's it, all. This is an evaluator, like Reuben's, With a few
more features, and it's shorter.
Okay, there it is (the above comment was in the original post). I've
never tried it, but it looks good. :-) BTW, if it does work you might
want to thank Gavin Peters... after all, he wrote it. I was just
interested when I saw it, and stored it along With a bunch of other
source-code tidbits I've git here...
}