Evaluating a string of simple mathematical expressions [closed]

Answer 1

Fortran 77 (gfortran dialect, now with g77 support)

Number of characters: 2059

Obfuscated version:

      function e(c)
      character*99 c
      character b
      real f(24)                
      integer i(24)             
      nf=0                      
      ni=0                      
 20   nf=kf(0.0,nf,f)
      ni=ki(43,ni,i)         
 30   if (isp(c).eq.1) goto 20
      h=fr(c)
 31   g=fp(nf,f)
      j=ip(ni,i)
      select case(j)
      case (40) 
         goto 20
      case (42)                 
         d=g*h
      case (43)                 
         d=g+h
      case (45)                 
         d=g-h
      case (47)                 
         d=g/h
      end select
 50   nf=kf(d,nf,f)
 60   j=nop(c)
      goto (20, 70, 75, 75, 60, 75, 60, 75) (j-39)
 65   e=fp(nf,f)
      return
 70   h=fp(nf,f)              
      goto 31
 75   ni=ki(j,ni,i)
      goto 30
      end
      function kf(v,n,f)
      real f(24)
      kf=n+1
      f(n+1)=v
      return
      end
      function ki(j,n,i)
      integer i(24)
      ki=n+1
      i(n+1)=j
      return
      end
      function fp(n,f)
      real f(24)
      fp=f(n)
      n=n-1
      return
      end
      function ip(n,i)
      integer i(24)
      ip=i(n)
      n=n-1
      return
      end
      function nop(s)
      character*99 s
      l=1
      do while(s(l:l).eq." ".and.l.lt.99)
         l=l+1
      enddo
      nop=ichar(s(l:l))
      s(l:l)=" "
      return
      end
      function isp(s)
      character*99 s
      isp=0
      l=1
      do while(s(l:l).eq." ".and.l.lt.99)
         l=l+1
      enddo
      isp=41-ichar(s(l:l))
      if (isp.eq.1) s(l:l)=" "
      return
      end
      function fr(s)
      character*99 s
      m=1                      
      n=1                      
      i=1
      do while(i.le.99)
         j=ichar(s(i:i))
         if (j.eq.32) goto 90   
         if (j.ge.48.and.j.lt.58) goto 89
         if (j.eq.43.or.j.eq.45) goto (89,80) m
         if (j.eq.46) goto (83,80) n
 80      exit
 83      n=2
 89      m=2
 90      i=i+1
      enddo
      read(s(1:i-1),*) fr
      do 91 j=1,i-1
         s(j:j)=" "
 91   continue
      return 
      end

Clear version: (3340 characters with scaffold)

      program infixeval
      character*99 c
      do while (.true.)
         do 10 i=1,99
            c(i:i)=" "
 10      continue
         read(*,"(A99)") c
         f=e(c)
         write(*,*)f
      enddo
      end

      function e(c)
      character*99 c
      character b
      real f(24)                ! value stack
      integer i(24)             ! operator stack
      nf=0                      ! number of items on the value stack
      ni=0                      ! number of items on the operator stack
 20   nf=pushf(0.0,nf,f)
      ni=pushi(43,ni,i)         ! ichar(+) = 43
D     write (*,*) "'",c,"'"
 30   if (isp(c).eq.1) goto 20
      h=fr(c)
D     write (*,*) "'",c,"'"
 31   g=fpop(nf,f)
      j=ipop(ni,i)
D     write(*,*) "Opperate ",g," ",char(j)," ",h
      select case(j)
      case (40) 
         goto 20
      case (42)                 ! "*" 
         d=g*h
      case (43)                 ! "+"
         d=g+h
      case (45)                 ! "-"
         d=g-h
      case (47)                 ! "*"
         d=g/h
      end select
 50   nf=pushf(d,nf,f)
 60   j=nop(c)
D     write(*,*) "Got op: ", char(j)
      goto (20, 70, 75, 75, 60, 75, 60, 75) (j-39)
 65   e=fpop(nf,f)
      return
 70   h=fpop(nf,f)              ! Encountered a "("
      goto 31
 75   ni=pushi(j,ni,i)
      goto 30
      end

c     push onto a real stack
c     OB as kf
      function pushf(v,n,f)
      real f(24)
      pushf=n+1
      f(n+1)=v
D     write(*,*) "Push ", v
      return
      end

c     push onto a integer stack
c     OB as ki
      function pushi(j,n,i)
      integer i(24)
      pushi=n+1
      i(n+1)=j
D     write(*,*) "Push ", char(j)
      return
      end

c     pop from real stack
c     OB as fp
      function fpop(n,f)
      real f(24)
      fpop=f(n)
      n=n-1
D      write (*,*) "Pop ", fpop
      return
      end

c     pop from integer stack
c     OB as ip
      function ipop(n,i)
      integer i(24)
      ipop=i(n)
      n=n-1
D      write (*,*) "Pop ", char(ipop)
      return
      end

c     Next OPerator: returns the next nonws character, and removes it
c     from the string
      function nop(s)
      character*99 s
      l=1
      do while(s(l:l).eq." ".and.l.lt.99)
         l=l+1
      enddo
      nop=ichar(s(l:l))
      s(l:l)=" "
      return
      end

c     IS an open Paren: return 1 if the next non-ws character is "("
c     (also overwrite it with a space. Otherwise return not 1
      function isp(s)
      character*99 s
      isp=0
      l=1
      do while(s(l:l).eq." ".and.l.lt.99)
         l=l+1
      enddo
      isp=41-ichar(s(l:l))
      if (isp.eq.1) s(l:l)=" "
      return
      end

c     Float Read: return the next real number in the string and removes the
c     character
      function fr(s)
      character*99 s
      m=1                      ! No sign (Minus or plus) so far
      n=1                      ! No decimal so far
      i=1
      do while(i.le.99)
         j=ichar(s(i:i))
         if (j.eq.32) goto 90   ! skip spaces
         if (j.ge.48.and.j.lt.58) goto 89
         if (j.eq.43.or.j.eq.45) goto (89,80) m
         if (j.eq.46) goto (83,80) n
c     not part of a number
 80      exit
 83      n=2
 89      m=2
 90      i=i+1
      enddo
      read(s(1:i-1),*) fr
      do 91 j=1,i-1
         s(j:j)=" "
 91   continue
      return 
      end

Notes This edited version is rather more evil than my first attempt. Same algorithm, but now inline with a horrible tangle of gotos. I've ditched the co-routines, but am now using a couple of flavors of computed branches. All error checking and reporting has been removed, but this version will silently recover from some classes of unexpected characters in the input. This version also compiles with g77.

The primary limits are still fortran's rigid formatting, long and ubiquitous keywords, and simple primitives.

Answer 2

SNOBOL4

Number of characters: 232

        a = pos(0) | '('
        n = span('0123456789.')
        j = '!+;!-;!*;!/;       output = e'
d       j '!' len(1) . y = "    e a . q n . l '" y "' n . r = q (l " y " r)     :s(p)"  :s(d)
        k = code(j)
        e = input
s       e ' ' = :s(s)
p       e ('(' n . i ')') = i   :s(p)f<k>
end

This is a semi-cheat. It uses code() (a variant of eval) to de-compress itself, but not to evaluate the input expression.

De-obfuscated version, without code:

        prefix = pos(0) | '('
        num = span('0123456789.')
        expr = input
spaces  expr ' ' = ''   :s(spaces)
paren   expr ('(' num . x ')') = x      :s(paren)
add     expr (prefix . pfx) (num . l) '+' (num . r) = pfx (l + r)       :s(paren)
sub     expr (prefix . pfx) (num . l) '-' (num . r) = pfx (l - r)       :s(paren)
mul     expr (prefix . pfx) (num . l) '*' (num . r) = pfx (l * r)       :s(paren)
div     expr (prefix . pfx) (num . l) '/' (num . r) = pfx (l / r)       :s(paren)
        output = expr
end

Strategy:

• First, remove all spaces (spaces)
• Whenever possible, remove parentheses surrounding a number (paren)
• Otherwise, find a simple expression involving two numbers, prefixed by '(' or at the start of the string
• If none of the above rules apply, the expression is fully evaluated. Now if the input was well formed we should be left with a number.

Example:

• 1 + (2 * 3) + 4
• 1+(2*3)+4 [spaces]
• 1+(6)+4 [mul]
• 1+6+4 [paren]
• 7+4 [add]
• 11 [add]

Answer 3

Python

Number of characters: 237

Fully obfuscated function:

from operator import*
def e(s,l=[]):
 if s:l+=list(s.replace(' ','')+')')
 a=0;o=add;d=dict(zip(')*+-/',(0,mul,o,sub,div)));p=l.pop
 while o:
  c=p(0)
  if c=='(':c=e(0)
  while l[0]not in d:c+=p(0)
  a=o(a,float(c));o=d[p(0)]
 return a

Clear/semi-obfuscated function:

import operator

def calc(source, stack=[]):
    if source:
        stack += list(source.replace(' ', '') + ')')

    answer = 0

    ops = {
        ')': 0,
        '*': operator.mul,
        '+': operator.add,
        '-': operator.sub,
        '/': operator.div,
    }

    op = operator.add
    while op:
        cur = stack.pop(0)

        if cur == '(':
            cur = calc(0)

        while stack[0] not in ops:
            cur += stack.pop(0)

        answer = op(answer, float(cur))
        op = ops[stack.pop(0)]

    return answer

Answer 4

Here comes another one:

Shell script (using sed+awk)

Number of characters: 295

obfuscated:

e(){ a="$1";while echo "$a"|grep -q \(;do eval "`echo "$a"|sed 's/\(.*\)(\([^()]*\))\(.*\)/a="\1\`e \"\2\"\`\3"/'`";done; echo "$a"|sed 's/\([-+*/]\) *\(-\?\) */ \1 \2/g'|awk '{t=$1;for(i=2;i<NF;i+=2){j=$(i+1);if($i=="+") t+=j; else if($i=="-") t-=j; else if($i=="*") t*=j; else t/=j}print t}';}

readable

e () {
    a="$1"
    # Recursively process bracket-expressions
    while echo "$a"|grep -q \(; do
        eval "`echo "$a"|
            sed 's/\(.*\)(\([^()]*\))\(.*\)/a="\1\`e \"\2\"\`\3"/'`"
    done
    # Compute expression without brackets
    echo "$a"|
        sed 's/\([-+*/]\) *\(-\?\) */ \1 \2/g'|
        awk '{
            t=$1;
            for(i=2;i<NF;i+=2){
                j=$(i+1);
                if($i=="+") t+=j;
                else if($i=="-") t-=j;
                else if($i=="*") t*=j;
                else t/=j
            }
            print t
        }'
}

Test:

str='  2.45 / 8.5  *  9.27   +    (   5   *  0.0023  ) '
echo "$str"|bc -l
e "$str"

Result:

2.68344117647058823526
2.68344

Answer 5

Visual Basic.NET

Number of characters: 9759

I'm more of a bowler myself.

NOTE: does not take nested parentheses into account. Also, untested, but I'm pretty sure it works.

Imports Microsoft.VisualBasic
Imports System.Text
Imports System.Collections.Generic
Public Class Main
Public Shared Function DoArithmaticFunctionFromStringInput(ByVal MathematicalString As String) As Double
    Dim numberList As New List(Of Number)
    Dim operationsList As New List(Of IOperatable)
    Dim currentNumber As New Number
    Dim currentParentheticalStatement As New Parenthetical
    Dim isInParentheticalMode As Boolean = False
    Dim allCharactersInString() As Char = MathematicalString.ToCharArray
    For Each mathChar In allCharactersInString
        If mathChar = Number.ZERO_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.ONE_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.TWO_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.THREE_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.FOUR_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.FIVE_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.SIX_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.SEVEN_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.EIGHT_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.NINE_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Number.DECIMAL_POINT_STRING_REPRESENTATION Then
            currentNumber.UpdateNumber(mathChar)
        ElseIf mathChar = Addition.ADDITION_STRING_REPRESENTATION Then
            Dim addition As New Addition

            If Not isInParentheticalMode Then
                operationsList.Add(addition)
                numberList.Add(currentNumber)
            Else
                currentParentheticalStatement.AllNumbers.Add(currentNumber)
                currentParentheticalStatement.AllOperators.Add(addition)
            End If

            currentNumber = New Number
        ElseIf mathChar = Number.NEGATIVE_NUMBER_STRING_REPRESENTATION Then
            If currentNumber.StringOfNumbers.Length > 0 Then
                currentNumber.UpdateNumber(mathChar)

                Dim subtraction As New Addition
                If Not isInParentheticalMode Then
                    operationsList.Add(subtraction)
                    numberList.Add(currentNumber)
                Else
                    currentParentheticalStatement.AllNumbers.Add(currentNumber)
                    currentParentheticalStatement.AllOperators.Add(subtraction)
                End If

                currentNumber = New Number
            Else
                currentNumber.UpdateNumber(mathChar)
            End If
        ElseIf mathChar = Multiplication.MULTIPLICATION_STRING_REPRESENTATION Then
            Dim multiplication As New Multiplication

            If Not isInParentheticalMode Then
                operationsList.Add(multiplication)
                numberList.Add(currentNumber)
            Else
                currentParentheticalStatement.AllNumbers.Add(currentNumber)
                currentParentheticalStatement.AllOperators.Add(multiplication)
            End If
            currentNumber = New Number
        ElseIf mathChar = Division.DIVISION_STRING_REPRESENTATION Then
            Dim division As New Division

            If Not isInParentheticalMode Then
                operationsList.Add(division)
                numberList.Add(currentNumber)
            Else
                currentParentheticalStatement.AllNumbers.Add(currentNumber)
                currentParentheticalStatement.AllOperators.Add(division)
            End If
            currentNumber = New Number
        ElseIf mathChar = Parenthetical.LEFT_PARENTHESIS_STRING_REPRESENTATION Then
            isInParentheticalMode = True
        ElseIf mathChar = Parenthetical.RIGHT_PARENTHESIS_STRING_REPRESENTATION Then
            currentNumber = currentParentheticalStatement.EvaluateParentheticalStatement
            numberList.Add(currentNumber)
            isInParentheticalMode = False
        End If
    Next

    Dim result As Double = 0
    Dim operationIndex As Integer = 0
    For Each numberOnWhichToPerformOperations As Number In numberList
        result = operationsList(operationIndex).PerformOperation(result, numberOnWhichToPerformOperations)
        operationIndex = operationIndex + 1
    Next

    Return result

End Function
Public Class Number
    Public Const DECIMAL_POINT_STRING_REPRESENTATION As Char = "."
    Public Const NEGATIVE_NUMBER_STRING_REPRESENTATION As Char = "-"
    Public Const ZERO_STRING_REPRESENTATION As Char = "0"
    Public Const ONE_STRING_REPRESENTATION As Char = "1"
    Public Const TWO_STRING_REPRESENTATION As Char = "2"
    Public Const THREE_STRING_REPRESENTATION As Char = "3"
    Public Const FOUR_STRING_REPRESENTATION As Char = "4"
    Public Const FIVE_STRING_REPRESENTATION As Char = "5"
    Public Const SIX_STRING_REPRESENTATION As Char = "6"
    Public Const SEVEN_STRING_REPRESENTATION As Char = "7"
    Public Const EIGHT_STRING_REPRESENTATION As Char = "8"
    Public Const NINE_STRING_REPRESENTATION As Char = "9"

    Private _isNegative As Boolean
    Public ReadOnly Property IsNegative() As Boolean
        Get
            Return _isNegative
        End Get
    End Property
    Public ReadOnly Property ActualNumber() As Double
        Get
            Dim result As String = ""
            If HasDecimal Then
                If DecimalIndex = StringOfNumbers.Length - 1 Then
                    result = StringOfNumbers.ToString
                Else
                    result = StringOfNumbers.Insert(DecimalIndex, DECIMAL_POINT_STRING_REPRESENTATION).ToString
                End If
            Else
                result = StringOfNumbers.ToString
            End If
            If IsNegative Then
                result = NEGATIVE_NUMBER_STRING_REPRESENTATION & result
            End If
            Return CType(result, Double)
        End Get
    End Property
    Private _hasDecimal As Boolean
    Public ReadOnly Property HasDecimal() As Boolean
        Get
            Return _hasDecimal
        End Get
    End Property
    Private _decimalIndex As Integer
    Public ReadOnly Property DecimalIndex() As Integer
        Get
            Return _decimalIndex
        End Get
    End Property
    Private _stringOfNumbers As New StringBuilder
    Public ReadOnly Property StringOfNumbers() As StringBuilder
        Get
            Return _stringOfNumbers
        End Get
    End Property
    Public Sub UpdateNumber(ByVal theDigitToAppend As Char)
        If IsNumeric(theDigitToAppend) Then
            Me._stringOfNumbers.Append(theDigitToAppend)
        ElseIf theDigitToAppend = DECIMAL_POINT_STRING_REPRESENTATION Then
            Me._hasDecimal = True
            Me._decimalIndex = Me._stringOfNumbers.Length
        ElseIf theDigitToAppend = NEGATIVE_NUMBER_STRING_REPRESENTATION Then
            Me._isNegative = Not Me._isNegative
        End If
    End Sub
    Public Shared Function ConvertDoubleToNumber(ByVal numberThatIsADouble As Double) As Number
        Dim numberResult As New Number
        For Each character As Char In numberThatIsADouble.ToString.ToCharArray
            numberResult.UpdateNumber(character)
        Next
        Return numberResult
    End Function
End Class
Public MustInherit Class Operation
    Protected _firstnumber As New Number
    Protected _secondnumber As New Number
    Public Property FirstNumber() As Number
        Get
            Return _firstnumber
        End Get
        Set(ByVal value As Number)
            _firstnumber = value
        End Set
    End Property
    Public Property SecondNumber() As Number
        Get
            Return _secondnumber
        End Get
        Set(ByVal value As Number)
            _secondnumber = value
        End Set
    End Property
End Class
Public Interface IOperatable
    Function PerformOperation(ByVal number1 As Double, ByVal number2 As Number) As Double
End Interface
Public Class Addition
    Inherits Operation
    Implements IOperatable
    Public Const ADDITION_STRING_REPRESENTATION As String = "+"
    Public Sub New()

    End Sub
    Public Function PerformOperation(ByVal number1 As Double, ByVal number2 As Number) As Double Implements IOperatable.PerformOperation
        Dim result As Double = 0
        result = number1 + number2.ActualNumber
        Return result
    End Function
End Class
Public Class Multiplication
    Inherits Operation
    Implements IOperatable
    Public Const MULTIPLICATION_STRING_REPRESENTATION As String = "*"
    Public Sub New()

    End Sub
    Public Function PerformOperation(ByVal number1 As Double, ByVal number2 As Number) As Double Implements IOperatable.PerformOperation
        Dim result As Double = 0
        result = number1 * number2.ActualNumber
        Return result
    End Function
End Class
Public Class Division
    Inherits Operation
    Implements IOperatable
    Public Const DIVISION_STRING_REPRESENTATION As String = "/"
    Public Const DIVIDE_BY_ZERO_ERROR_MESSAGE As String = "I took a lot of time to write this program. Please don't be a child and try to defile it by dividing by zero. Nobody thinks you are funny."
    Public Sub New()

    End Sub
    Public Function PerformOperation(ByVal number1 As Double, ByVal number2 As Number) As Double Implements IOperatable.PerformOperation
        If Not number2.ActualNumber = 0 Then
            Dim result As Double = 0
            result = number1 / number2.ActualNumber
            Return result
        Else
            Dim divideByZeroException As New Exception(DIVIDE_BY_ZERO_ERROR_MESSAGE)
            Throw divideByZeroException
        End If
    End Function
End Class
Public Class Parenthetical
    Public Const LEFT_PARENTHESIS_STRING_REPRESENTATION As String = "("
    Public Const RIGHT_PARENTHESIS_STRING_REPRESENTATION As String = ")"
    Private _allNumbers As New List(Of Number)
    Public Property AllNumbers() As List(Of Number)
        Get
            Return _allNumbers
        End Get
        Set(ByVal value As List(Of Number))
            _allNumbers = value
        End Set
    End Property
    Private _allOperators As New List(Of IOperatable)
    Public Property AllOperators() As List(Of IOperatable)
        Get
            Return _allOperators
        End Get
        Set(ByVal value As List(Of IOperatable))
            _allOperators = value
        End Set
    End Property
    Public Sub New()

    End Sub
    Public Function EvaluateParentheticalStatement() As Number
        Dim result As Double = 0
        Dim operationIndex As Integer = 0
        For Each numberOnWhichToPerformOperations As Number In AllNumbers
            result = AllOperators(operationIndex).PerformOperation(result, numberOnWhichToPerformOperations)
            operationIndex = operationIndex + 1
        Next

        Dim numberToReturn As New Number
        numberToReturn = Number.ConvertDoubleToNumber(result)
        Return numberToReturn
    End Function
End Class
End Class

Answer 6

Ruby 1.9

(because of the regex)

Number of characters: 296

def d(s)
  while m = s.match(/((?<pg>\((?:\\[()]|[^()]|\g<pg>)*\)))/)
    s.sub!(m[:pg], d(m[:pg][1,m[:pg].size-2]))
  end
  while m = s.match(/(-?\d+(\.\d+)?)\s*([*+\-\/])\s*(-?\d+(\.\d+)?)/)
    r=m[1].to_f.send(m[3],m[4].to_f) if %w{+ - * /}.include?m[3]
    s.sub!(m[0], r.to_s)
  end
  s
end

EDIT: Includes Martin's optimization.