Public Function ToRoman(ByVal vnNumber As Integer) As String
    Do While vnNumber >= 1000
        ToRoman = ToRoman & "M"
        vnNumber = vnNumber - 1000
    Loop
    If vnNumber >= 900 Then
        ToRoman = ToRoman & "CM"
        vnNumber = vnNumber - 900
    End If
    If vnNumber >= 500 Then
        ToRoman = ToRoman & "D"
        vnNumber = vnNumber - 500
    ElseIf vnNumber >= 400 Then
        ToRoman = ToRoman & "CD"
        vnNumber = vnNumber - 400
    End If
    Do While vnNumber >= 100
        ToRoman = ToRoman & "C"
        vnNumber = vnNumber - 100
    Loop
    If vnNumber >= 90 Then
        ToRoman = ToRoman & "XC"
        vnNumber = vnNumber - 90
    End If
    If vnNumber >= 50 Then
        ToRoman = ToRoman & "L"
        vnNumber = vnNumber - 50
    ElseIf vnNumber >= 40 Then
        ToRoman = ToRoman & "XL"
        vnNumber = vnNumber - 40
    End If
    Do While vnNumber >= 10
        ToRoman = ToRoman & "X"
        vnNumber = vnNumber - 10
    Loop
    If vnNumber = 9 Then
        ToRoman = ToRoman & "IX"
    Else
        If vnNumber >= 5 Then
            ToRoman = ToRoman & "V"
            vnNumber = vnNumber - 5
        End If
        If vnNumber = 4 Then
            ToRoman = ToRoman & "IV"
        Else
            Do While vnNumber >= 1
                ToRoman = ToRoman & "I"
                vnNumber = vnNumber - 1
            Loop
        End If
    End If
End Function 
By Renfield

package require Tcl 8.5 
 namespace path ::tcl::mathop
# Chiffre Arabe vers Romain
proc romain {n} { 
      set resultat {} 
      foreach {chiffre valeur} { 
         M 1000 CM 900 D 500 CD 400 C 100 XC 90 
          L 50 XL 40 X 10 IX 9 V 5 IV 4 I 1 
      } { 
         append resultat [string repeat $chiffre [/ $n $valeur]] 
         set n [% $n $valeur] 
      } 
      return $resultat 
 
} 
 
# Chiffre Romain vers Arabe


proc niamor {romain} { 
      + {*}[string map { 
         IV {4 } IX {9 } XL {40 } XC {90 } CD {400 } CM {900 } 
         I {1 } V {5 } X {10 } L {50 } C {100 } D {500 } M {1000 } 
      } $romain] 
 
} 
 

puts [romain 1881] 
 puts [niamor CCLV]

BASIC_ROMAN_NUMBERS = [ "M", "CM", "D", "CD", "C", "XC",
            "L", "VL", "XL", "X", "IX", "V", "IV", "I" ]
BASIC_VALUES = [ 1000, 900, 500, 400, 100, 90,
        50, 45, 40, 10, 9, 5, 4, 1 ]
def int2rom(val):
    remainder=val
    s=''
    if val<1 or val>3999: return "ERROR"
    for i in range(len(BASIC_VALUES)):
    while remainder>=BASIC_VALUES[i]:
        s+=BASIC_ROMAN_NUMBERS[i]
        remainder -= BASIC_VALUES[i]
    return s
def rom2int(s):
    index=0
    value=0
    for i in range(len(BASIC_ROMAN_NUMBERS)):
    sRom= BASIC_ROMAN_NUMBERS[i]
    lensRom=len(sRom)
    while s[index:index+lensRom]==sRom:
        value += BASIC_VALUES[i]
        index += lensRom
    if int2rom(value)!="ERROR":
    return value
    else: return "%s: ILLEGAL ROMAN NUMBER => %d?"%(s,value)
print '1492 %s' %int2rom(1492) #=> abrege: MCDXCII ok
print '1854 %s' %rom2int('MDCCCLIV') #=> 1854 ok
print '45a %s' %rom2int('VL') #45 abbrege ok
print '1911a %s' %rom2int('MCMXI') #1911 abrege ok