Get the base address of your executable.
Create a snapshot of the modules inside of assault cube, and grab the base address of your executable. HINT: TlHelp32.h.
First grab the process (CreateToolhelp32Snapshot, TH32CS_SNAPPROCESS), get a handle to assault cube (OpenProcess), then grab the module (CreateToolhelp32Snapshot, TH32CS_SNAPMODULE) and get the base address of the module "ac_client.exe". Yes, it is counted as a module.
Once you got that, you can ReadProcessMemory:
Code:
ReadProcessMemory(MyHandle, (LPVOID)(BaseAddressOfModule + Offset), &MyBuffer, sizeof(MyBuffer), NULL);
If you need help, ask here.
To everyone else, please do not provide copy paste ready code as OP is trying to learn.