A simple example of how to manipulate the value of a memory address of another process.

First off, compile the programs using gcc.
Spin up the target and get its pid
Go into gdb using the pid of the target gdb -p <pid>
In gdb, find the memory address of the variable: p &secret, and copy it
Finally, run the injector with the pid and the address of the variable: ./injector <pid> <address>

This'll only work if the variable is not in the stack or in the register, hence why we're placing it outside of the main scope.