What Is a Pointer?

Big idea

A pointer is a variable that stores an address — where another variable lives in memory. & gets an address; * follows one.

The idea

Every variable sits somewhere in memory, and every spot in memory has a numbered address. You've already used one: scanf("%d", &age) hands scanf the address of age.

int score = 90;
int *p = &score;

• int *p — p is a pointer to an int: it holds the address of an int.
• &score — "the address of score".
• Now p points to score.

Follow the pointer with *:

printf("%d\n", *p);   // 90 — the value at the address in p
*p = 95;              // changes score, through the pointer

Watch it

(Real addresses are longer and change every run — these are shortened to read easily.)

Watch a pointer move

See real addresses

%p prints an address. Run it twice — the numbers change, but &x and p always match:

#include <stdio.h>

int main(void) {
    int x = 7;
    int *p = &x;
    printf("&x = %p\n", (void *) &x);
    printf("p  = %p\n", (void *) p);
    printf("*p = %d\n", *p);
    return 0;
}

The two meanings of *

• In a declaration, * makes a pointer type: int *p;
• In an expression, * follows the pointer: *p = 5;

Common mistake

Using a pointer before pointing it anywhere. An uninitialised pointer holds a random address; writing through it can crash or silently corrupt other data. Point it at something first — or set it to NULL (address zero, "points nowhere") and check before use:

int *p = NULL;
if (p != NULL) {
    *p = 5;
}

Think of it like

A contact card with someone's home address. The card isn't the house — but by following the address you can visit the house and even repaint the door.

🕷️ Spidey-sense: My spider-tracer doesn't hold the villain — it holds where the villain is. Follow the tracer (*), and I'm right there. Pointers: with great power comes great responsibility.

Key terms

• Address — The location of a variable in memory.
• Pointer — A variable holding an address.
• & (address-of) — Gets a variable's address.
• * (dereference) — Follows a pointer to the value it points at.
• NULL — A pointer that points nowhere.