Pointer Basics

A pointer is a house address

A normal variable is like a house holding a value. A pointer is a piece of paper with that house's address written on it — not the house itself.

& and * — address-of and dereference

&x gives the address of x. *p reads (or writes) the value at the address p holds.

int x = 10;
int *p = &x;      // p holds x's address

printf("%d\n", x);   // 10
printf("%d\n", *p);  // 10 -- value at that address

*p = 20;              // change x through p
printf("%d\n", x);   // 20

Output:

10
10
20

Declared type matters

int *p means "p points to an int", not "*p is int". The * in a declaration is part of the pointer's type, telling C how many bytes to read/write through it.