What is the difference between stack and heap memory in C++?

C++ programs use two main memory regions: Stack memory: fast, automatically managed, LIFO (Last In First Out). Local variables, function parameters, return addresses, and register saves are placed on the stack. void foo() { int x = 42; // Stack -- x lives until foo() returns Car c("Toyota", 2022); // Stack -- c destroyed at } } // x and c automatically destroyed here. Characteristics: allocated and freed automatically (function call/return); very fast (just move stack pointer); limited size (typically 1-8MB — stack overflow if exceeded); all variables destroyed when scope ends. Heap memory (Free Store): manual management, dynamically sized, large. Car* c = new Car("Toyota", 2022); // Heap -- exists until deleted c->drive(); delete c; // Must manually free! auto sp = std::make_unique<Car>("Honda"); // Heap via smart ptr. Characteristics: you control lifetime (allocate with new, free with delete/smart ptr); slower than stack (calls allocator, may need to search free blocks); large (limited by RAM/virtual memory); NOT automatically freed — forgetting delete = memory leak. When to use each: stack for small, short-lived data (primitives, small objects); heap for: large objects (can't fit in stack), unknown size at compile time (vectors, user input), objects that must outlive their creating function, sharing between parts of the program. Memory layout: Code → Data (globals) → Heap (grows up) ... Stack (grows down). Stack and heap grow toward each other — if they meet, crash.