What is the difference between declaring with new and without it?

Question

C++ / C#

In addition, the construction with new allows you to manually free the memory later

Answer 1

POSITION IN MEMORY
Without new: static/global - in the data segment, local - on the stack. In the data segment, memory is allocated during compilation by linking, creating a stack frame is two processor commands.
With new: on the heap. Heap management is quite a difficult task, and if there are a lot of these new, the program can start to slow down.
LIFETIME
Without new: the object lives while execution is in the given block. When the block is exited, the destructor automatically fires.
With new: Destroy whenever we want.
NAME
Without new: the object is bound to its name.
With new: the object is unnamed (only the pointer has a name). Therefore, data structures of variable size are possible: dynamic arrays, linked lists, trees, and so on.
SIZE
Without new: given at compile time. That is, an array of 10 positions, and a point, more - only by recompilation.
With new: arbitrary.

Answer 2

new allocates memory on the heap, while a definition without new allocates on the stack, with all its advantages and disadvantages. You need to understand when to define an object on the heap, and when on the stack.