How to find a memory location with a dynamic address?

Question

reverse engineering

Little by little I study reverse engineering, I wrote a program that, when a key is pressed, adds some number to a variable and outputs the result to the console and tries to "hack" it. The essence of the problem: I can’t figure out how to find something that will make it possible to work with a variable from the outside without looking for its address manually every time the program is restarted. I tried to look for offsets and static pointers, it did not work. I would very much like to look at manuals for dummies where they disassemble the hacking of such simple programs, if any.