我应该将程序从C更新为现代C或C ++吗？

I have an old program written in C from the 1990's. I would like to update it so that it will work for the next persons and on modern compilers. Currently I am using a really old version of TurboC to make changes. Should I be focusing on rewriting this in modern C or C++? Which will be the easiest to bring this code up to date without having to rewrite too much and be able to reuse most of the existing code?I have an old program written in C from the 199