Fundamentals of Programming: Algorithms, C Language Basics, Tokens, and Operators

Algorithms and Pseudocode

• Algorithm: A step-by-step procedure or set of precise, unambiguous instructions executed in finite time to accomplish a task.
  • Derived from the phonetic pronunciation of the last name of Arabic mathematician Abu Ja'far Mohammed ibn Musa al-Khowarizmi.
  • Must feature precise inputs, outputs, a start instruction, and a stop instruction without requiring computer-specific code.
• Pseudocode: An informal, artificial English-like language used to plan algorithms prior to coding in target languages like C. It cannot be executed directly on computers.
• Control Constructs:
  • SEQUENCE: Linear execution of sequential tasks.
  • WHILE: Loop with a condition evaluated at the beginning.
  • REPEAT-UNTIL: Loop with a condition evaluated at the bottom.
  • FOR: Loop governed by iteration bounds.
  • IF-THEN-ELSE: Conditional branching statement.
  • CASE: Generalization of the multi-way IF-THEN-ELSE statement.

Flowcharts

• Flowchart: A diagrammatic tool depicting the step-by-step process flow of a program using geometric shapes connected by arrows.

• Core Symbols & Functions:
  • Terminal (Oval / Capsule): Marks the system starting or ending point.
  • Process (Rectangle): Represents internal processor, memory, or action steps.
  • Input/Output (Parallelogram): Represents data entry or result output operations.
  • Decision (Diamond): Asks a binary question resulting in branching paths (Yes/No, True/False).
  • Connector (Circle): Connects breaks in a flowchart without intersecting lines or reverse flow.
  • Predefined Process: Invokes a subroutine or an interrupt program.
  • Preparation (Hexagon): Represents setup prior to another step.
  • Flow Lines (Arrows): Indicate direction of flow.
• General Rules:
  • Standard direction flows top-to-bottom. Upward flow must not exceed $3$ symbols.
  • Symbols have an entry point at the top and an exit point at the bottom, except Decision symbols which have two exit points.

C Language Overview and Development Cycle

• Origins: Developed in $1972$ at Bell laboratories by Dennis M. Ritchie to implement the UNIX operating system (derived from B / BCPL). First implemented on the DEC PDP-11 computer.
  • In $1978$, Dennis Ritchie and Brian Kernighan published The C Programming Language ("K & R C").
  • ANSI C standard was completed in $1988$ (committee formed in $1983$).
• Standard Features: Portability, Flexibility, Modularity, Robustness, Extensibility, Efficiency and effectiveness.
• Development Cycle:
  1. Creating: Code is written using a text editor and saved as a source file.
  2. Compiling: Compiler translates source file into machine code and checks syntax.
  3. Linking: Linker combines object code with library functions (e.g., header files like stdio.h).
  4. Executing: Operating system's Program Loader loads the .EXE file into RAM for run-time execution.
• C vs C++ Differences:
  • C: Procedural programming language; no support for OOPs, function overloading, operator overloading, or access control mechanisms. Uses manual memory management (malloc(), calloc(), free()).
  • C++: Supports Procedural, Object-Oriented, and Generic paradigms. Supports OOPs concepts, function overloading, operator overloading, access control keywords (private, public, protected), and automatic/manual memory handling (new, delete).

C Tokens, Identifiers, and Data Types

• Tokens: Smallest individual building blocks recognized by the compiler:
  • Keywords: $32$ pre-defined, reserved lowercase words performing specific system functions (e.g., int, return, void, if, while).
  • Identifiers: Custom names assigned to variables, functions, and arrays. Must begin with an alphabet or underscore (_), contain only alphanumeric characters, and are case-sensitive.
  • Variables: Named memory locations storing dynamic values. Must be declared before use.
• Basic Data Types:
  • int (%d or %i): Whole integer numbers.
  • float (%f): Real numbers with decimal points.
  • double (%f): Large numbers with decimal points.
  • char (%c): Single letter/symbol enclosed in single quotes.
  • char array (%s): Series of characters forming a string enclosed in double quotes.

C Operators

• Arithmetic: + (Addition), - (Subtraction), * (Multiplication), / (Division), % (Modulo division for remainder).
• Relational: == (Equal to), > (Greater than), < (Less than), != (Not equal to), >= (Greater than or equal to), <= (Less than or equal to). Returns true ($1$) or false ($0$).
• Logical: && (Logical AND), || (Logical OR), ! (Logical NOT).
• Bitwise / Binary:
  • & (AND), | (OR), ^ (EX-OR), ~ (Bitwise complement: $-(n + 1)$).
  • << (Left shift): Left shifting once multiplies value by $2$.
  • >> (Right shift): Right shifting once divides value by $2$.
• Assignment: =, +=, -=, *=, /=, %=, <<=, >>=, &=, |=, ^=.
• Increment / Decrement:
  • ++operand (Unary pre-increment): Increments value first, then assigns.
  • --operand (Unary pre-decrement): Decrements value first, then assigns.
  • operand++ (Unary post-increment): Assigns value first, then increments.
  • operand-- (Unary post-decrement): Assigns value first, then decrements.