Pointer Introduction

To understand pointers, you first need to understand how C views memory. Think of your computer's RAM as a long street with many houses. Each house has a House Number (the Address) and People living inside (the Value).

1. The Core Concept

A Pointer is a variable that stores the memory address of another variable. Instead of holding a piece of data (like the number 5), it holds the "GPS coordinates" to where that 5 is located.

The Two Special Symbols

• & (Address-of operator): This gets the memory address of a variable.
• * (Dereference operator / Value-at-address): This allows you to look inside the address a pointer is holding.

In C programming, every variable is stored in the computer’s memory (RAM).

Memory can be imagined as a long street of houses.

• Each house represents a memory location
• Each house has:
  • A house number → called the memory address
  • A person living inside → called the value

When we create a variable in C:

int age = 25;

• The value 25 is stored in a memory location
• That memory location has a unique address
• Normally, we only use the value, not the address

Why Are Pointers Needed?

Pointers are required because:

• Memory addresses are important in C
• Functions need access to original variables
• Large data should not be copied
• Dynamic memory is needed at runtime

Without pointers, C cannot work efficiently with memory

2. A Visual Example

Imagine we have an integer variable age.

1#include <stdio.h>
2
3int main() {
4    int age = 25;      // A regular integer
5    int *ptr;          // A POINTER variable (note the * in declaration)
6
7    ptr = &age;        // Store the address of 'age' into 'ptr'
8
9    printf("Value of age: %d\n", age);          // Output: 25
10    printf("Address of age: %p\n", &age);       // Output: 0x7ffe... (the memory location)
11    printf("Value stored in ptr: %p\n", ptr);   // Output: 0x7ffe... (the same address)
12    printf("Value pointed to by ptr: %d\n", *ptr); // Output: 25 (Dereferencing)
13
14    return 0;
15}

3. Step-by-Step Breakdown

1. Declaration (int *ptr;): The * here tells C, "This variable isn't going to hold a normal number; it’s going to hold the address of an integer."
2. Assignment (ptr = &age;): We use the & symbol to grab the physical location of age in the RAM and save it into ptr.
3. Dereferencing (*ptr): When we use * on an existing pointer, it says: "Follow the address stored in ptr and tell me what value is sitting there."

4. Why use Pointers?

Students often ask, "Why not just use the variable name?" Here are three main reasons you will encounter as you progress:

• Efficiency: Instead of passing a massive amount of data (like a giant array) to a function, you just pass one small pointer (the address).
• Modifying Variables: As seen in the "Swap" example earlier, pointers allow a function to change a variable that exists outside of that function.
• Dynamic Memory: Pointers allow you to request more memory while the program is actually running (using malloc).

5. Summary Table for Quick Reference