2. Pointer Basics

2.1 Declaring Pointers 
 Syntax: 
 data_type *pointer_name;
 
 Examples: 
 int *ptr; // Pointer to an integer
float *fptr; // Pointer to a float
char *cptr; // Pointer to a character
double *dptr; // Pointer to a double
 
 Important Notes: 
 
 The * (asterisk) indicates that the variable is a pointer 
 The asterisk can be placed next to the type or the variable name 
 All three declarations below are equivalent:
 int *ptr;
int* ptr;
int * ptr;
 
 
 Convention: Most C programmers use int *ptr style 
 
 Multiple Pointer Declaration: 
 int *p1, *p2, *p3; // Three pointers to int
int *p1, p2, *p3; // p1 and p3 are pointers, p2 is int
int* p1, p2, p3; // Only p1 is pointer! p2 and p3 are int
 
 2.2 Pointer Operators 
 There are two main operators for working with pointers: 
 
 
 
 Operator 
 Name 
 Description 
 Example 
 
 
 
 
 & 
 Address-of 
 Gets the memory address of a variable 
 &variable 
 
 
 * 
 Dereference 
 Accesses the value at the address stored in pointer 
 *pointer 
 
 
 
 2.3 Initializing Pointers 
 Method 1: Initialize with address of existing variable 
 int num = 42;
int *ptr = # // ptr now points to num
 
 Method 2: Initialize to NULL 
 int *ptr = NULL; // Pointer points to nothing (safe initialization)
 
 Method 3: Uninitialized (DANGEROUS) 
 int *ptr; // Contains garbage value - DO NOT USE until initialized!
 
 Visual Representation: 
 Memory Layout:

Variable: num = 42
Address: 0x1000
 ┌──────┐
0x1000: │ 42 │ num
 └──────┘

Variable: ptr
Address: 0x2000
 ┌────────┐
0x2000: │ 0x1000 │ ptr (points to num)
 └────────┘
 
 2.4 Using Pointers - The & and * Operators 
 #include <stdio.h>

int main() {
 int num = 100;
 int *ptr;
 
 ptr = &num; // Store address of num in ptr
 
 printf("Value of num: %d\n", num); // Direct access
 printf("Address of num: %p\n", (void*)&num); // Address of num
 printf("Value of ptr: %p\n", (void*)ptr); // Address stored in ptr
 printf("Value pointed to by ptr: %d\n", *ptr); // Dereference ptr
 
 // Modify through pointer
 *ptr = 200;
 
 printf("\nAfter *ptr = 200:\n");
 printf("Value of num: %d\n", num); // num changed!
 printf("Value pointed to by ptr: %d\n", *ptr);
 
 return 0;
}

/* Output:
Value of num: 100
Address of num: 0x7ffd5c8e4a3c
Value of ptr: 0x7ffd5c8e4a3c
Value pointed to by ptr: 100

After *ptr = 200:
Value of num: 200
Value pointed to by ptr: 200
*/
 
 Understanding the Operations: 
 int num = 42;
int *ptr = &num;

// These are equivalent:
num = 100; // Direct modification
*ptr = 100; // Indirect modification through pointer

// Both operations change the same memory location