I have been trying to study coding since then, so chose Python since its praised for it's simplicity. Had to check up the thread and so this. Mind you I know nothing about C nor C++ but got curious and searched about your question and came across this https://siv2r.hashnode.dev/big-integer-arithmetic-in-c-part-1 which I found interesting at first but got complicated when I got to the coding section. I believe you would be able to gain something from why and how to  define a 256bit in C its similar to what @PowerGlove stated though.