Tell how memory is allocated on the stack and in the heap. Are all value types always placed on the stack?

In C#, memory on the stack is allocated very quickly and simply: when a method is called, a block of memory for local variables is allocated on the stack, which is freed when exiting the method. The stack operates on a LIFO principle.

The heap is a memory area for reference type objects and some value types that do not fit on the stack (for example, large structures or objects placed inside classes). The heap is managed by the garbage collector.

Value types (structs) are usually placed on the stack if they are local variables or method parameters. But if a value type is a field of a reference type (class) or is inside a closure, it is placed on the heap.

Example:

struct Point { public int X, Y; }

void Method() {
    Point p = new Point(); // p on the stack
    var obj = new Wrapper { P = p }; // obj on the heap, p inside obj also on the heap
}

class Wrapper {
    public Point P;
}

Thus, value types are not always on the stack — their placement depends on the context of use.