Postfix evalution function.

-=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- (c) WidthPadding Industries 1987 0\|604\|0 -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=-
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Dan	Created : 12 September 2020 Edited : 19 September 2020 Postfix evalution function.
Hi, this is my try at the postfix evaluation. Global stackmax=100, stackpos=0, postfixmax=100, postpos=0, postitems=0, stackerror=0 Dim stack$(stackmax) Dim postfix$(postfixmax) ;***** demo ******** Dim calc$(10) calc$(00)="1 2 + 3 * 6 + 2 3 + /" ;Answer 3 calc$(01)="2.2 7.0 + 3.0 " ;Answer 27.6 calc$(02)="1 3 5 + - " ;Answer -7 calc$(03)="3 4 / 5.0 +" ;Answer 5.0 calc$(04)="3 4.0 / 5.0 +" ;Answer 5.75 calc$(05)="-3 -4 +" ;Answer -7 calc$(06)="-3.0 3 " ;Answer -9.0 calc$(07)="3 4 2 * 1 5 - 2 3 ^ ^ / +" ;Answer 3.00012 calc$(08)="1 2 + 3 4 + 5 6 + + +" ;Answer 21 calc$(09)="4 0.0 /" ;Div by 0 calc$(10)="3 5 7 4 - 2 ^ * +" ;48.0 For x=0 To 10 If calc$(x)="" Then Exit StrToPostfixArray(calc$(x)) Write PostfixEval$() + " " : DebugLog("") If stackerror>0 Then Print ": " + ErrToText$(stackerror) : Else Print "" : stackerror=0 Next WaitKey() End ;***** /demo ******** ;Error numbers: ;#1: Stack overflow ;#2: Stack empty ;#3: Stack not empty ;#4: Not a number ;#5: division by zero ;#6: stack underflow Function StrToPostfixArray(in$) ;Converts a string containing a postfix notation into an postfix$ array ;Rule: Numbers and operators have to be separated by " " Local tmpx, tmptxt$, txt$ , i=0 postitems=0 For tmpx=1 To Len(in$) tmptxt$=Mid$(in$,tmpx,1) If tmptxt$="-" And i=0 i=i+1 : txt$=txt$+tmptxt$ Else If tmptxt$=" " And i>0 Then postfix$(postitems)=txt$ : postitems=postitems+1 : i=0 : txt$="" If tmptxt$<>" " Then i=i+1 : txt$=txt$+tmptxt$ EndIf Next If i>0 Then postfix$(postitems)=txt$ : postitems=postitems+1 : i=0 : txt$="" End Function Function PostfixEval$() ;Fill up the postfix$ array with items before calling this function, set postitems to number of items ;e.g 3 2 + = 3 items ;Currently accepted are + - * / ^ and numbers ;Stackerror #3 - Stack not empty, #4 - a non number is on the stack, #5 division by zero Local x, t$ ,a$, b$ stackpos=0 stackerror=0 For x=0 To postitems-1 t$=postfix$(x) ;DebugLog "Stack ("+StackItems(2)+ ")" Select t$ Case "+" b$=Pop() : a$=Pop() If stackerror=0 If isFloat(a$,b$)=0 Push(Int(a$)+Int(b$)) Else Push(Float(a$)+Float(b$)) EndIf EndIf Case "-" b$=Pop() : a$=Pop() If stackerror=0 If isFloat(a$,b$)=0 Push(Int(a$)-Int(b$)) Else Push(Float(a$)-Float(b$)) EndIf EndIf Case "" b$=Pop() : a$=Pop() If stackerror=0 If isFloat(a$,b$)=0 Push(Int(a$)Int(b$)) Else Push(Float(a$)*Float(b$)) EndIf EndIf Case "/" b$=Pop() : a$=Pop() If stackerror=0 If isFloat(a$,b$)=0 If Int(b$)=0 Then stackerror=5 Else Push(Int(a$)/Int(b$)) EndIf Else If Float(b$)=0 Then stackerror=5 Else Push(Float(a$)/Float(b$)) EndIf EndIf EndIf Case "^" b$=Pop() : a$=Pop() If stackerror=0 If isFloat(a$,b$)=0 Push(Int(a$)^Int(b$)) Else Push(Float(a$)^Float(b$)) EndIf EndIf Default If isNumber(t$) : Push (t$) : Else : stackerror=4 : EndIf End Select If stackerror>0 Then Exit Next If stackerror>0 StackItems$(1) ;Clear the stack Return "Err "+stackerror EndIf a$=Pop() If StackItems$()>0 And stackerror=0 Then stackerror=3 : a$="Err 3" : stackpos=0 ;Check if the stack is greater than 1 (pos 0 contains the result) StackItems$(1) Return a$ End Function Function StackItems$(clear=0) Local a$="",x If clear=0 Return stackpos ;Returns number of items in the stack ElseIf clear=1 For x=0 To stackmax-1 ;Clear the stack stack$(x)="" Next stackpos=0 ElseIf clear=2 For x=0 To stackmax-1 ;Display the stack items If stack$(x)>"" Then a$=a$+stack$(x)+" " Next Return a$ ElseIf clear=-1 ;Return the stack items sticked together For x=0 To stackmax-1 If stack$(x)<>"" Then a$=a$+stack$(x) Next Return a$ Else Return "what" EndIf End Function Function Push$(txt$) DebugLog stackpos+" :Push "+txt$ ;After calling push, check if stackerror is 0 and remember to reset it ;Stack error - #1: Stack full, #6: stack underflow If stackpos>stackmax-1 Then stackerror=1 : Return "Err 1" If stackpos<0 Then stackerror=6 : Return "Err 6" stack$(stackpos)=txt$ stackpos=stackpos+1 End Function Function Pop$() ;After calling pop, check if stackerror is 0 and remember to reset it ;stack error - #2: Stack empty stackpos=stackpos-1 If stackpos=-1 Then stackerror=2 : Return "Err 2" Local nr$ nr$=stack$(stackpos) DebugLog stackpos+" :pop "+nr$ stack$(stackpos)="" Return nr$ End Function Function isFloat$(nr0$,nr1$="",nr2$="",nr3$="",nr4$="") Local c=0 If Instr(nr0$,".") Then c=1 If Instr(nr1$,".") Then c=1 If Instr(nr2$,".") Then c=1 If Instr(nr3$,".") Then c=1 If Instr(nr4$,".") Then c=1 Return c End Function Function isNumber(nr$) ;check if nr$ is a number. At least it works O.o Local C$="+-.0123456789e", a=0, b=0 b=Len(nr$) If b=0 Return 0 For x=1 To b If Instr(C$,Mid$(nr,x,1)) Then a=a+1 Next If a=b Then Return 1 Return 0 End Function Function ErrToText$(nr) Local a$="" Select nr Case 1 : a$="Stack overflow." Case 2 : a$="Stack is empty." Case 3 : a$="Stack is not empty." Case 4 : a$="Not a number." Case 5 : a$="Division by zero." Case 6 : a$="Stack underflow" End Select Return a$ End Function --v

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Saturday, 19 September 2020, 06:31
Dan	Parsing mathematical expressions has never been easier ! (p.s. there is no error checking) (although it does not mean that writing such a parser was easy) Graphics 640,600,32,2 Graphics 320,250,32,3 Include "Postfix_eval_function.bb" Global infmax=200, infixitem=0 Dim infix$(infmax) Gosub demo Goto theend ;***** demo ******** .demo ; a$="10": strtoinfix(a$) : Gosub display a$="10+20" : strtoinfix(a$) : Gosub display a$="10+-20" : strtoinfix(a$) : Gosub display a$="10+--20" : strtoinfix(a$) : Gosub display a$="-10+(-20)" : strtoinfix(a$) : Gosub display a$="0+(2030)" : strtoinfix(a$) : Gosub display a$="0+(20-30)" : strtoinfix(a$) : Gosub display a$="10+(20/-30)/-10" : strtoinfix(a$) : Gosub display a$="+++10+((+$20/-!30)----10)" : strtoinfix(a$) : Gosub display a$="10^2" : strtoinfix(a$) : Gosub display a$="10+(-20)" : strtoinfix(a$) : Gosub display Repeat a$=Input$(">") strtoinfix(a$) : Gosub display Until a$="" Goto theend .display Locate 0,0: Cls Print a$ : Print For x=0 To infixitem-1 Print infix(x) Next ClearInfixArr() WaitKey() Return ;***** /demo ******** .theend End Function ClearInfixArr() For x=0 To infixitem infix(x)="" Next infixitem=0 End Function Function strtoinfix(txt$) Print txt$ ;i - input is being added ;j - type of input (numbers-1 or operators-2) ;o = was last operator plus or minus Local l, s=0, t=0, a, b, c, d, x, y, z, t1$="", t2$="" l=Len(txt$) For x=1 To l ;Parser t1$=Mid$(txt$,x,1) a=iSPlusMinus(t1$) b=isSeparator(t1$) If b=1 Then If s>0 Then Push(t2$) : t2$="" : s=0 Push(t1$) a=1 Else s=s+1 t2$=t2$+t1$ a=0 EndIf Next If a=0 Then Push(t2$) z=StackItems$(0) y=0 : s=0 : c=0 ;s track if 1st start, ;c count the +- Repeat y=y+1 t1$=StackPeek(y) a=iSPlusMinus(t1$) b=isSeparator(t1$) ;Stop If b=1 ;Deals with a=0 : c=0 : d=0 ;If t1$=")" Then Stop ;"+ + + x + ( ( x / - x ) - - - - x )" If Instr("()/^",t1$)=0 For x=y+1 To z+1 t2$=StackPeek(x) a=iSPlusMinus(t2$) b=isSeparator(t2$) If b=1 And a=0 Then d=1 : Exit ;it is another separator, but it is not + -, save it If a=1 Then c=c+1: ;it is another +- If b=0 Then d=2 : Exit ;number Next Else d=1 s=0 EndIf If d=1 ;Separator infix(infixitem)=t1$ infixitem=infixitem+1 If Instr("()/^",t1$)>0 Then If t1$<>")" Then s=0 Else s=1 Else For x=y+1 To y+c+1 t1$=StackPeek(x) infix(infixitem)=t1$ infixitem=infixitem+1 Next y=y+c+1 s=0 EndIf ElseIf d=2 ;Number If s=0 ;if s=0 then copy all of the separators and the number into the infix t1$="" For x=y To y+c+1 t1$=t1$+StackPeek(x) Next infix(infixitem)=t1$ infixitem=infixitem+1 y=y+c+1 s=1 Else ;copy the 1st P/M into infix, then each PM+number infix(infixitem)=t1$ infixitem=infixitem+1 t1$="" For x=y+s To y+c+s t1$=t1$+StackPeek(x) Next infix(infixitem)=t1$ infixitem=infixitem+1 y=y+c+1 EndIf ; Else ;Else ; Print "doh is short for Doughnut" EndIf Else ;it is a number infix(infixitem)=t1$ infixitem=infixitem+1 s=1 EndIf Until y>=z StackItems(1) End Function Function StackPeek$(nr) If nr<1 Or nr>stackmax-1 Then Return "" Return stack$(nr-1) End Function Function iSPlusMinus(txt$) Local c$="+-" Return (Instr(c$,Right$(txt$,1))>0) End Function Function isSeparator(txt$) Local c$="+-*/^()" Return (Instr(c$,txt$)>0) End Function --v The include file is the code from the 1st post. (you can remove the demo part of it, to test the code)

Postfix evalution function.

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