C LANGUAGE

🌟 C Language – Inventory & Versions

This page covers the history, versions, syntax, data types, variables, constants, and operators in C with examples.

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1. Inventory (History & Origin)

Year	Event
1969–1972	Developed by Dennis Ritchie at Bell Labs as a system programming language for UNIX.
1978	K&R C (first edition of The C Programming Language book published).
1989	ANSI C (C89) standard approved by ANSI.
1990	ISO C (C90) standardized internationally.
1999	C99 update introduced inline functions, variable-length arrays, // comments, and more.
2011	C11 introduced multi-threading support, Unicode handling, bounds-checking functions.
2018	C18 (minor revision of C11) — bug fixes and clarifications.

2. Why Use C?

• Foundation of programming – base for languages like C++, Java, C#.
• System-level programming – OS, compilers, embedded systems.
• Portable – runs on almost any hardware.
• Performance – faster execution with low-level memory access.

3. Advantages of C

1. Portable – works on different machines.
2. Structured – modular programming support.
3. Rich library – many built-in functions.
4. Memory control – direct pointer manipulation.
5. Fast execution – compiled directly to machine code.

4. Versions Summary

Version	Year	Main Features
K&R C	1978	Original syntax & features.
ANSI C (C89)	1989	Standardized syntax, function prototypes, new keywords.
ISO C (C90)	1990	International standard with fixes.
C99	1999	Inline functions, variable-length arrays, long long int, // comments.
C11	2011	Multi-threading, Unicode, _Static_assert.
C18	2018	Minor bug fixes and clarifications.

📌 Basic Syntax in C

Syntax is the rule of writing C programs. If you break rules, you get errors.

#include <stdio.h> // Header file
int main() { // main function
printf("Hello, World!");
return 0;
}

Output:
Hello, World!

• Every statement ends with ;
• main() is the starting point
• { } group statements
• #include adds header files

📌 Output in C

Output is the result displayed after running the program.

#include <stdio.h>
int main() {
printf("I am learning C");
return 0;
}

Output:
I am learning C

📌 Comments in C

Comments are ignored by compiler, used for explaining code.

Types:

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

#include <stdio.h>
int main() {
// Printing a message
printf("Backbenchers learn fast!");
/* This is
multi-line comment */
return 0;
}

Output:
Backbenchers learn fast!

📌 Data Types in C

Data types tell what kind of data a variable can store and memory size.

Type	Size
char	1 byte
int	4 bytes
float	4 bytes
double	8 bytes
long long int	8 bytes

#include <stdio.h>
int main() {
int age = 20;
char grade = 'A';
float pi = 3.14;
double bigPi = 3.14159265;
printf("Age: %d\\n", age);
printf("Grade: %c\\n", grade);
printf("PI: %.2f\\n", pi);
printf("PI (double): %.8lf", bigPi);
return 0;
}

Output:
Age: 20
Grade: A
PI: 3.14
PI (double): 3.14159265

📌 Keywords in C

Keywords are reserved words that cannot be used as identifiers.

Example: int number = 5; → here int is a keyword.

Some keywords:

auto, break, case, char, const, continue, default, do, else, enum, extern, float, for, goto, if, int, long, return, short

📌 Variables in C

A variable is a named memory location to store data.

Rules:

• Must start with letter or underscore
• Case-sensitive
• No spaces, no keywords
• Should be meaningful

#include <stdio.h>
int main() {
int age = 20;
float price = 99.50;
char grade = 'A';
printf("Age: %d\\n", age);
printf("Price: %.2f\\n", price);
printf("Grade: %c", grade);
return 0;
}

Output:
Age: 20
Price: 99.50
Grade: A

📌 Constants in C

Constants are fixed values that cannot be changed during execution.

• Integer constants: 10, -45, 0
• Floating-point: 3.14, -0.001
• Character: 'A', 'z'
• String: "Hello"

#define PI 3.1416
const int age = 18;

📌 Operators in C

Operators perform operations on variables and values.

• Arithmetic: +, -, *, /, %
• Relational: ==, !=, >, <, >=, <=
• Logical: &&, ||, !
• Assignment: =, +=, -=, *=, /=
• Increment/Decrement: ++, --
• Bitwise: &, |, ^, ~, <<, >>
• Ternary: (condition) ? true : false