Fix a compilation error

Need to include the cstdio header file to get access too stderr and fprintf on standards-conforming compilers.
Fix long to bigint assignment

Need to clear out the old value before adding the digits of the new one.
Fix a compilation error

Need to include the cstdio header file to get access too stderr and fprintf on standards-conforming compilers.
Fix long to bigint assignment

Need to clear out the old value before adding the digits of the new one.
Merge pull request #2 from ahtotruu/patch-1

Bugfix in long to bigint assignment