Arduino Memory FULL, I don't know why

[MicroBahner]

@cyphonvoid

I don't understand what do you mean by I didn't use C variable because I initialized it as 6 but do you mean I didn't use that in any of the functions?

Yes you initialized the variable, but you never used that value anywhere in the program. That's why the compiler dropped it.

@cyphonvoid

if I do ptr3 = &C is that considered using C or not

Of course it's a C/C++ assignment. Because you use the address of the variable C, the compiler cannot drop it anymore.