Introduction To C Language

Introduction to c language

🧾 History of C Language

C Language was developed in the early 1970s by Dennis Ritchie at Bell Laboratories (AT&T). It was created as an evolution of the B language, and it was initially used to develop the UNIX operating system.

Milestones:

1972: C was developed
1978: "The C Programming Language" book by Brian Kernighan and Dennis Ritchie was published
1989: ANSI standardized C as "ANSI C"
Later: ISO standards followed, leading to C90, C99, C11, and C18

Why It Matters: C is considered the foundation of many modern programming languages like C++, Java, and Python due to its speed, control, and portability.

🏗️ Structure of a C Program

A C program follows a specific and well-organized structure. Understanding its parts helps in writing, debugging, and managing code easily.

Typical Structure Includes:

Header Files Inclusion: Using #include to import libraries like stdio.h, math.h
Global Declarations: Variables, constants, or functions defined outside main()
Main Function: Starting point of execution — int main()
Variable Declaration: Inside functions to define local data
Executable Statements: The actual logic and instructions
Functions: Optional — reusable blocks of code

Example:

#include <stdio.h>

int main() {
    printf("Hello, World!");
    return 0;
}

🧩 Functions as Building Blocks

Functions are self-contained blocks of code designed to perform a specific task. In C, they help in modularizing the program.

Advantages of Functions:

Code reusability
Improved readability and maintainability
Debugging and testing becomes easier
Supports top-down programming

Types of Functions:

Library Functions: Predefined (e.g., printf(), sqrt())
User-defined Functions: Created by the programmer

Function Syntax:

return_type function_name(parameters) {
    // code
}

Example:

int add(int a, int b) {
    return a + b;
}

language fundamentals

🔤 Character Set

Character set in C includes all valid characters that can be used in programs. It includes:

Letters: A–Z, a–z
Digits: 0–9
Special Characters: +, -, *, /, %, =, &, |, <,>, ^, etc.
Whitespace: space, tab, newline

🔹 C Tokens

Tokens are the smallest individual units in a C program. These are:

Keywords
Identifiers
Constants
Strings
Operators
Special Symbols

🔑 Keywords

Keywords are reserved words that have predefined meanings in C. They cannot be used as identifiers (e.g., variable names).

Examples: int, return, if, while, for, void, char

C has 32 standard keywords.

🆔 Identifiers

Identifiers are the names given to variables, functions, arrays, etc., by the programmer.

Rules:

Must begin with a letter (A–Z or a–z) or underscore (_)
Cannot be a keyword
Can contain letters, digits, and underscores
Case-sensitive

📦 Variables

Variables are named memory locations used to store data that can change during program execution.

Syntax: data_type variable_name;

Example: int age;, float salary;

🔒 Constants

Constants are fixed values that do not change during program execution.

Types of Constants:

Integer constants: e.g., 10, -25
Floating-point constants: e.g., 3.14, -0.5
Character constants: e.g., 'A', '3'
String constants: e.g., "Hello", "123"

Defining constant: #define PI 3.14 or const int x = 10;

📊 Data Types

Data types define the type of data a variable can hold in C.

Primary Data Types:

int – Integer values (e.g., 5, -3)
float – Floating-point numbers (e.g., 3.14)
char – Single character (e.g., 'A')
double – Double-precision float

Derived Types: Arrays, Pointers, Structures, Unions

💬 Comments

Comments are non-executable statements used to explain code. They help improve code readability.

Types of Comments:

Single-line: // This is a comment
Multi-line: /* This is a multi-line comment */