Stack vs Heap, new and delete

This unit is the heart of C++'s reputation, good and bad. Where a value lives decides how long it exists, how fast it is to allocate, and who must clean it up. Every segfault war story, every garbage-collector pause in other languages, and a large share of systems-interview questions trace back to the distinction on this page.

Two places your data can live

The stack. Every function call gets a stack frame: a slab of memory holding its parameters and local variables. When the function returns, the frame is popped and every variable in it dies instantly. All the locals you have written so far lived here. Stack memory is automatic and extremely fast, but small (a few MB) and tied to scope.

The heap. A big pool of memory you request at run time. Heap data survives until you explicitly free it, no matter how many functions return in the meantime. The price: you are the garbage collector.

int* makeCounter() {
    int local = 0;          // stack: dies when makeCounter returns
    int* h = new int(0);    // heap: survives the return
    return h;               // caller receives the address
}

new int(0) allocates one int on the heap, initializes it to 0, and returns its address. Later, someone must call delete on that address, or the memory is lost until the program exits: a memory leak.

Python note: every Python object lives on a heap, and the garbage collector frees it for you. C++ gives you the choice, and the responsibility.