Pointers

Introduction

A pointer variable records an address. With & and * you can link functions, arrays, and heap blocks without copying large payloads.

Understanding the topic

Declaration int *p; — p holds an address.

Address-of & &x gives address of x.

Dereference * *p gives value at address p.

• Declaration — int *p; — p holds an address.
• Address-of & — &x gives address of x.
• Dereference * — *p gives value at address p.

Step-by-step explanation

1. Declaration — int *p; — p holds an address.
2. Address-of & — &x gives address of x.
3. Dereference * — *p gives value at address p.

Syntax reference

Syntax reference:

type *ptr;
ptr = &variable;
*ptr = value;

Informative example

Example program:

#include <stdio.h>

int main(void) {
    int n = 17;
    int *ptr = &n;
    printf("val=%d at=%p\n", *ptr, (void*)ptr);
    return 0;
}

Execution workflow

Best practices

• Enable warnings: gcc -Wall -Wextra -std=c11 source.c -o app
• Give every variable a defined value before it is read.
• Stay inside array bounds — C will not stop you from over-running a buffer.

Common mistakes

• Reading uninitialized storage — behavior is undefined.
• Dismissing compiler warnings instead of fixing root causes.
• Ignoring NULL returns from malloc, fopen, and similar APIs.

Hands-on exercise

Practice problems:

• Pointer to int
• Modify value through pointer
• Null pointer check

Summary

Pointers in C — Address variables that tie together memory, arrays, and functions.