CALU: a basic char based arithmetic calculator (in progress)

A little test program I'm writing that's not dependent on actual integers but rather using string based numbers, breaking the 4.29b/18.4t limit
It's being built for Windows and Linux, and is completely C standard library compliant
So far, I just got fully working addition to work and it will only do math with positive numbers
The way digits work is dynamic but have a static limit, so for example, 100+100000 shifts the digits for 100 to the right
These number strings can also have padded zeroes
Currently, I have this program set to support 256 digits

code:
https://github.com/donnaken15/CALU/blob/main/CALU.C
man:
https://github.com/donnaken15/CALU/blob/main/CALU.1