Pointers in C Programming

Pointers

• A pointer is a variable that stores the memory address of another variable.
• Declared using the asterisk symbol (*) before the pointer name.
• Example: int *ptr; declares a pointer to an integer.
• Pointer operators:
  • & (address-of operator): returns the memory address of a variable.
  • * (dereference operator): returns the value stored at a memory address.
• Pointer arithmetic:
  • Incrementing/decrementing a pointer moves it to the next/previous memory location.
  • Pointers can be compared using relational operators.
• Common pointer operations:
  • Dynamic memory allocation: malloc(), calloc(), realloc(), free().
  • Pointer casting: converting a pointer to a different data type.

Data Structures

• Arrays:
  • A collection of elements of the same data type stored in contiguous memory locations.
  • Declared using type array_name[size];.
  • Example: int scores[5]; declares an array of 5 integers.
• Structures:
  • A collection of variables of different data types stored together.
  • Declared using the struct keyword.
  • Example: struct student { int id; char name[20]; };.
• Linked Lists:
  • A dynamic collection of nodes, each containing a value and a reference to the next node.
  • Nodes are allocated dynamically using malloc().
  • Example: a singly linked list of integers.

Algorithm Design

• Asymptotic Notation:
  • Big O, Ω, and Θ notations used to describe an algorithm's time and space complexity.
  • Examples:
    • O(1) - constant time complexity.
    • O(n) - linear time complexity.
    • O(n^2) - quadratic time complexity.
• Algorithm Design Techniques:
  • Divide and Conquer: break down a problem into smaller sub-problems.
  • Dynamic Programming: break down a problem into smaller sub-problems and store solutions to sub-problems.
  • Greedy Algorithm: make the locally optimal choice at each step.

File Input/Output

• File Modes:
  • r - read mode.
  • w - write mode (truncates file if it exists).
  • a - append mode.
  • r+, w+, a+ - read and write modes.
• File Pointers:
  • FILE *fp; declares a file pointer.
  • fopen(): opens a file and returns a file pointer.
  • fclose(): closes a file.
• File Input/Output Functions:
  • fread(): reads from a file.
  • fwrite(): writes to a file.
  • fgetc(): reads a single character from a file.
  • fputc(): writes a single character to a file.

Pointers

• A pointer is a variable that stores the memory address of another variable.
• Declared using the asterisk symbol (*) before the pointer name.
• The & operator returns the memory address of a variable.
• The * operator returns the value stored at a memory address.
• Pointer arithmetic allows incrementing/decrementing a pointer to move to the next/previous memory location.
• Pointers can be compared using relational operators.

Data Structures

Arrays

• A collection of elements of the same data type stored in contiguous memory locations.
• Declared using type array_name[size];.
• Example: int scores[5]; declares an array of 5 integers.

Structures

• A collection of variables of different data types stored together.
• Declared using the struct keyword.
• Example: struct student { int id; char name; }; declares a structure with an integer and a character.

Linked Lists

• A dynamic collection of nodes, each containing a value and a reference to the next node.
• Nodes are allocated dynamically using malloc().
• Example: a singly linked list of integers.

Algorithm Design

Asymptotic Notation

• Big O, Ω, and Θ notations are used to describe an algorithm's time and space complexity.
• Examples: O(1) - constant time complexity, O(n) - linear time complexity, O(n^2) - quadratic time complexity.

Algorithm Design Techniques

• Divide and Conquer: break down a problem into smaller sub-problems.
• Dynamic Programming: break down a problem into smaller sub-problems and store solutions to sub-problems.
• Greedy Algorithm: make the locally optimal choice at each step.

File Input/Output

File Modes

• r - read mode.
• w - write mode (truncates file if it exists).
• a - append mode.
• r+, w+, a+ - read and write modes.

File Pointers

• FILE *fp; declares a file pointer.
• fopen(): opens a file and returns a file pointer.
• fclose(): closes a file.

File Input/Output Functions

• fread(): reads from a file.
• fwrite(): writes to a file.
• fgetc(): reads a single character from a file.
• fputc(): writes a single character to a file.