Formula parser - Printable Version

Code:
function ParseEq(byval eq as string) as double

    dim as integer curLow=4,curInd,numOfOps=0,numOfPar=1

    

    'filter spaces

    for c = 0 to len(eq)-1 

        if eq[c]=32 then eq=left$(eq,c)+right$(eq,len(eq)-c-1)        

    next c

    

    'get rid of parantheses if they include the whole equation 'ex (234+434*(23+1)) ->  234+434*(23+1) 

    if eq[0]=40 and eq[len(eq)-1]=41 then

        for c = 1 to len(eq)-1            

            if eq[c]=41 or eq[c]=40 then numOfPar+=(40-eq[c])*2+1            

            if numOfPar=0 and c<>len(eq)-1 then exit for

            if numOfPar=0 and c=len(eq)-1 then eq=mid$(eq,2,len(eq)-2)

        next

    end if

    

    'find the lowest operator

    for c = 0 to len(eq)-1 

        

        'skip stuff inside parantheses in the operation count

        if eq[c]=40 then '( 

            numOfPar=1

            for tempc = c+1 to len(eq)-1

                if eq[tempc]=41 or eq[tempc]=40 then numOfPar+=(40-eq[tempc])*2+1            

                c=tempc+1

                if numOfPar=0 then exit for                

            next

            if c=len(eq) then exit for 'equation end has been reached            

        end if

        

        if eq[c]=43 or eq[c]=45 or eq[c]=42 or eq[c]=47 or eq[c]=94 then numOfOps+=1

        if eq[c]=43 or eq[c]=45 then '+,-

            curLow=44-eq[c]

            curInd=c        

        elseif eq[c]=42 or eq[c]=47 then '*,/

            if abs(curLow) > 1 then

                curLow=-((eq[c]-42)/5*4-2)

                curInd=c

            end if         

        elseif eq[c]=94 then '^

            if abs(curLow) > 2 then

                curLow=3

                curInd=c

            end if          

        end if

    next

    if numOfOps=0 then return val(eq)'single number, no equation to evaluate!

    if abs(curLow)= 1 then return ParseEq(left$(eq,curInd)) + ParseEq(right$(eq,len(eq)-curInd-1))*curLow 'split formula into two formulas, the split being at the lowest operation

    if curLow= 2 then return ParseEq(left$(eq,curInd)) * ParseEq(right$(eq,len(eq)-curInd-1))

    if curLow=-2 then return ParseEq(left$(eq,curInd)) / ParseEq(right$(eq,len(eq)-curInd-1))

    if curLow= 3 then return ParseEq(left$(eq,curInd)) ^ ParseEq(right$(eq,len(eq)-curInd-1))    

end function



dim as string eq

eq="(10  ^(2*2))/20+(  90*4)*10+ (1+9)*88  +244  /866-  46^  2-1"

print (10 ^(2*2))/20+( 90*4)*10+ (1+9)*88 +244 /866- 46^ 2-1

print ParseEq(eq)

sleep