C and C++ require explicit dynamic memory management, using new and delete or malloc() and free().
It is helpful to understand where variables exist (usually the stack or the heap, sometimes the data segment 1).
The stack is managed for you by the compiler, so it's usually the easiest memory to use. Local variables go on the stack, and passed function parameters go on the stack2. Since the stack frame can change signi?cantly between uses, do not return pointers to the stack! This is analogous to dereferencing freed memory.
If a variable needs to exist longer than a function call, then you should put allocate space for it on the heap (with new, for instance). If you allocate space for a variable, remember to free that space when you're done with it! If you allocate memory but don't free it, you'll end up with memory leaks, which usually becomes a problem when a program is supposed to run for a long time, repeatedly allocating and forgetting to free. It can be helpful to write allocating functions/methods at the same time as freeing functions/methods, so that you don't forget to deallocate memory from the heap.