Addresses and Pointer Variables

Memory as numbered houses

Every byte of memory has an address — a number, like a house number on a very long street. A variable like int x = 42; occupies some of those houses. The address-of operator & asks "where does x live?"

int x = 42;
printf("%p\n", (void*)&x);   // e.g. 0x7ffe... — an address, different each run

A pointer stores an address

A pointer is just a variable whose value is an address:

int x = 42;
int *p = &x;        // p holds the address of x

Read int *p as "p is a pointer to int". The type matters: an int* promises "the object at this address is an int". A double* promises a double. Pointers to different types are not interchangeable.

Two spellings, one meaning

int *p;             // declaration context: * says "p is a pointer"
*p = 7;             // expression context:  * means "the object p points to"

Address is not value

x is 42. &x is where 42 lives. p is a copy of that where. Three different things. Keeping them straight is 80% of understanding pointers.