C$++$: Number Conversion $-$ Roman Numerals

here are some example Expected output:

What file? LXXXVII $=87$

CCXIX $=219$

MCCCLIV $=1354$

CXXX$***2$ the same and the next bigger $***$

MMDCLXXIII $=2673$

DXL$***$ Two subtractions in a row $***$

MCDLXXVI $=1476$

X$***$ Invalid character in input file $***$

X $=10$

IV $=4$

here is another one

Expected output:

What file? MMMCMXCIX $=3999$

CCVII $=207$

XXXIX $=39$

XXXIX$***$ Invalid character in input file $***$

MDCCLXXVI $=1776$