We start with C language because:

1. It is a basic and powerful language.

2. It helps us understand:

   • Memory

   • How computers work internally

   • Logic building

3. Many modern languages are based on C.

4. It is widely used in:

   • Operating Systems

   • Embedded Systems

   • System Programming

• BCPL (Basic Combined Programming Language) was developed by
  Martin Richards in 1967.

• From BCPL, a new language called B language was developed by
  Ken Thompson.

• Later, C language was developed from B language by
  Dennis Ritchie in 1972 at
  Bell Labs.

So 
C language is a modified and improved version of B language.

C language was created by:

• Dennis Ritchie → Known as the Father of C language

• Brian Kernighan → Helped in documenting and popularizing C

C language was developed at:

• Bell Labs (USA)
  Bell Labs was owned by AT&T

C language was developed in 1972.

C is still popular because:

a. Versatility (All-rounder Language)

C can be used to develop:

• System Software (like Operating Systems)

• Application Software

b. Fast and Efficient

• C programs run very fast.

• It gives direct access to memory.

c. Foundation Language

• Many modern languages like:

  • C++

  • Java

  • Python
    are influenced by C.

d. Used in Important Systems

• Operating Systems

• Embedded Systems

• Device Drivers

• Compilers

 That’s why C is still called an “All-rounder” and “Mother language of many languages.”

#include <stdio.h>   // Standard Input Output header file
#include <conio.h>   // Console Input Output header file (for getch(), clrscr(), etc.)

void main() {
   // This is the main function from where execution starts
   printf("Hello User");  // Prints message on the screen
   getch();        // Waits for user to press a key
}

A header file in C programming is a file that contains predefined functions, macros, constants, and type definitions that you can use in your program. Header files usually have the extension .h, for example:

• stdio.h – for input/output functions like printf() and scanf().
• math.h – for mathematical functions like sqrt(), pow(), sin(), and cos().
• conio.h – for console input/output functions like getch() and clrscr().

Think of a header file as a toolbox for C programmers. Instead of writing all the code from scratch, you can include these “tools” in your program to save time and effort.

Why Do We Use Header Files in C?

Including header files in C programming is essential for several reasons:

1. Access Predefined Functions
   Header files contain functions that are already written and tested. For example, without including stdio.h, you cannot use printf() or scanf() in your program.
2. Simplify Programming
   Header files allow you to write code faster because you don’t need to reinvent the wheel. All standard functions are available at your fingertips.
3. Avoid Errors
   When you include a header file, the compiler knows the function prototypes (what arguments they take and what value they return). This prevents compilation errors.
4. Code Reusability
   Header files promote modular programming. You can write reusable functions in separate header files and include them in multiple programs.
5. Better Organization
   Large programs can be split into multiple header files to keep the code clean, organized, and easier to maintain.

When Should You Include a Header File?

You should include a header file whenever your program uses functions, constants, or types that are defined outside your program. Some common examples include:

Syntax to include a header file:

Example: Simple C Program Using a Header File

Here:

• #include <stdio.h> allows the program to use printf().
• Without including this header, the compiler would not recognize printf() and give an error.

In C programming, the stdio.h header file is one of the most important and widely used header files. The term stdio stands for Standard Input Output, which basically means it allows your program to take input from the user (keyboard) and display output on the screen (monitor).

Key Functions of stdio.h

The stdio.h header file provides functions that handle essential input and output operations in C. The most commonly used functions include:

1. printf() – This function is used for output, i.e., displaying text, variables, or results on the screen.

    

   printf("Hello, World!\n");

2. scanf() – This function is used for input, i.e., accepting data from the user via the keyboard.

    

   int age;
   scanf("%d", &age);

Why is stdio.h Important?

• Essential for Almost Every Program:
  Almost every C program involves input and output, making stdio.h necessary for nearly all projects.
• Simplifies Programming:
  Without stdio.h, programmers would have to write complex code to handle keyboard input and screen output manually.
• Standardized Functions:
  Functions like printf() and scanf() are predefined, tested, and optimized, making coding faster and error-free.

Example: Using stdio.h

Explanation:

1. #include <stdio.h> → Includes standard input/output functions.
2. printf() → Displays a message on the screen.
3. scanf() → Reads input from the user.

In C programming, conio.h is a header file that stands for CONSOLE Input Output.

Here’s what that means:

• Console – The window where your program displays output and interacts with the user. This could be the command prompt or terminal on your operating system.
• Input/Output – conio.h provides functions to take input from the keyboard and control the console output, making your program more interactive and visually appealing.

 Note: The console window itself is not created by conio.h; it is generated by the operating system (like DOS or Windows). conio.h just gives you the tools to control it.

Important Functions of conio.h

1. clrscr() – Clears the console window and removes all previous outputs.

    

   clrscr(); // Clear the screen

2. textcolor(color) – Changes the font color of text in the console window.

    

   textcolor(RED); // Set text color to red

3. getch() – Pauses the console window until a key is pressed.

    

   getch(); // Wait for user input

4. gotoxy(x, y) – Moves the cursor to a specific position on the console.

    

   gotoxy(10, 5); // Move cursor to column 10, row 5

Why Use conio.h?

• Better Control of Console Output: Change text colors, move the cursor, or clear the screen for a cleaner interface.
• Pause Program Execution: Useful for letting the user see results before the console closes.
• Interactive Programming: Makes your program visually appealing and easy to follow, especially for beginner projects or small games.

Example Program Using conio.h

In the C programming language, the symbol # is called a pound sign (also known as hash).

 Any line in a C program that begins with # is called a Preprocessor Directive.

 What are Preprocessor Directives?

Preprocessor directives are special instructions that are processed before compilation.

a. They are handled by a special program called the C Preprocessor, not by the compiler.
b. The preprocessor runs before the compiler and prepares the code for compilation.

 Role of the C Preprocessor

The preprocessor performs tasks like:

• Including files
• Defining macros
• Conditional compilation
• Removing comments

 It only processes lines that start with #.

 What is #include?

#include is a file inclusion directive.

 It tells the preprocessor to include the content of another file into the program.

Example:

a. This line includes the standard input-output library
b. It allows functions like printf() and scanf() to work

 Types of #include

1. System File

 Searches in standard library folders

2. User-defined File

 Searches in the current directory

 Popular Preprocessor Directives in C

1. File Inclusion

 Used to include header files

2. Macro Definition

 Defines a macro (constant or expression)

3. Macro Undefinition

 Removes a previously defined macro

4. Conditional Compilation

These directives control compilation based on conditions:

 Useful for:

• Debugging
• Platform-specific code
• Feature toggling

 Why do we use Preprocessor Directives?

a. To make code reusable
b. To simplify complex code
c. To improve readability
d. To control compilation

A function in C language is a named block of code that performs a specific task.

 It consists of:

• A function name
• A pair of parentheses ()
• A set of instructions enclosed in curly braces {}

Example:

a. Functions help in breaking a program into smaller, manageable parts
b. They improve code readability and reusability

 What is the main() Function in C?

 Every C program must have a main() function.

 a. It is the starting point of program execution
b. The Operating System (OS) always begins execution from main()

 Importance of main() Function

•  It acts like the entry point of the program
•  Execution of the program always starts from main()
•  Without main(), the program cannot run

 Think of main() as the engine of a car 
Just like a car starts with an engine, a C program starts with main().

 Structure of main() Function

int → return type
return 0; → indicates successful execution

 Can We Compile a C Program Without main()?

   Yes, we can compile it, but…

a.  Compilation is done by the compiler
b.  The compiler checks syntax from top to bottom
c. It does not require main() to compile

 Can We Run a Program Without main()?

No, we cannot run it ❌

a.  Execution is handled by the Operating System (OS)
b.  The OS always starts execution from the main() function
c.  If main() is missing → program will not run

 Key Difference (Important )

Compilation is the process of converting source code (written in C language) into machine code (binary code).

a)  Source code → Human-readable
b)  Machine code → Computer-readable (0s and 1s)

 Why is Compilation Important?

 Computers (CPU) do not understand C language directly.

a)  They only understand binary language (0 and 1)
b)  So, we must convert our program into machine code

 This conversion process is called Compilation

 What is a Compiler?

 A compiler is a software that performs compilation.

a>  It converts the entire program at once
b>  It checks for syntax errors
c>  It generates machine code (object/executable file)

 Compilation Process (Step by Step)

 Example

Source Code:

After Compilation:

 Converted into binary like:

 This binary code is what the computer executes

 Key Points (Exam Ready )

• Compilation = Source Code → Machine Code
• Done by a Compiler
• Computers understand only binary (0 & 1)
• It checks for errors before execution
• It is required before running a program

 Simple Definition (1 Line)

Compilation is the process of converting C source code into machine code using a compiler.

Integer Data Types

 Character Data Types

 How Values Are Stored in Memory?

 Every value stored in RAM is converted into binary form (0s and 1s).

Example:

• Decimal value: 25
• Binary value: 11001

 So internally:

 Computers store and process only binary data

 Integer Storage Example

 Stored in memory as:

 Character Storage & ASCII Value

 Characters are stored using ASCII (American Standard Code for Information Interchange)

Example:

• 'A' → ASCII = 65
• 'B' → ASCII = 66

 So:

 Important Points

• Every value in RAM is stored in binary form
• Characters are stored using ASCII codes
• ASCII converts characters → numbers → binary

 Program: Display Character and its ASCII Value

 Correct & Clean Code:

Sample Output

1️⃣ What is ASCII?

ASCII stands for American Standard Code for Information Interchange.
It is a coding standard used to represent characters as numbers in computers.

• Every character (letters, digits, symbols) has a unique ASCII value.
• For example:
  • A → 65
  • a → 97
  • 0 → 48

2️⃣ ASCII Ranges

There are 256 ASCII characters divided into two main ranges:

So, in total, there are 256 possible characters in the extended ASCII table.

3️⃣ Characters You Can See vs Special Ones

• Characters on a normal keyboard: A, B, C, a, b, c, 0, 1, 2, !, @, #
• Characters not usually visible: Special symbols like ☻, ♦, ║ or accented letters.

These are important when you want to display symbols directly using ASCII values in your C program.

4️⃣ Writing a C Program to Display ASCII Characters

Here’s a corrected and clean version of your program. I’ll explain each line for beginners.

5️⃣ Step-by-Step Explanation

1. unsigned char ch;
   • char stores characters.
   • unsigned allows it to store values from 0–255 (good for extended ASCII).
2. clrscr();
   • Clears the screen (optional, but makes output neat).
3. ch = 251;
   • Assigns an ASCII value.
   • Value 251 in extended ASCII represents √ in some systems (depends on your console font).
4. printf("Symbol: %c\nASCII Value: %d", ch, ch);
   • %c prints the character itself.
   • %d prints its numeric ASCII value.
5. getch();
   • Pauses the program so you can see the output.

In C programming, floating-point numbers are used to store decimal numbers like 3.14 or -0.0002.

There are three main types:

1️⃣ How Floating-Point Numbers are Stored

• Float numbers are not stored exactly in memory.
• C does not handle floats directly in the CPU. Instead, it uses FPE (Floating Point Emulator).

FPE is developed based on IEEE standards by the Institute of Electrical and Electronics Engineers (IEEE).

The number is stored as:

1. Mantissa (M) – the significant digits of the number
2. Exponent (E) – the scale or magnitude

Because of this approximation and compression, floats can store huge numbers in just 4 bytes, but their values might not be exact.

2️⃣ Important Points About Float

1. Approximation

   • Example:

      

     float x = 45.8;
     printf("%f", x);

     Output might be something like: 45.79999924

     • Not exactly 45.8 due to internal representation.
2. Cannot use wrong format specifiers

   • Example:

      

     float x = 65.0;
     printf("%d", x); // ❌ Will print garbage

     ✅ Correct usage:

      

     printf("%f", x); // Will print 65.000000

      
3. Integers and characters can be printed as %d

   • Example:

      

     char ch = 'A';
     printf("%d", ch); // 65 (ASCII value of 'A')
     int n = 65;
     printf("%c", n); // 'A' (ASCII character)

      
   • But the reverse does not work for floats.
4. No signed or unsigned modifier for float
   • Floats can be negative, but you cannot declare unsigned float.

3️⃣ Why Floats are Approximate

• Computers store floats in binary, not decimal.
• Some decimal numbers cannot be represented exactly in binary.
• That’s why 0.1 + 0.2 may not equal exactly 0.3 in C.

Always remember: Float ≈ Approximation, Not Exact

4️⃣ Best Practices

1. Use float for small precision numbers

    

   float pi = 3.14;

2. Use double for higher precision calculations

    

   double pi = 3.141592653589793;

    
3. Use %f, %lf, %Lf correctly
   • %f → float
   • %lf → double
   • %Lf → long double

5️⃣ Example Program

Output:

Notice how float is approximate, double is more precise, and long double can store even bigger numbers.

Operators are special symbols in C used to perform operations on variables or values.

• Example:

Think of operators as action symbols. They tell the computer: “Do this calculation, comparison, or check for me.”

 Types of Operators in C

C language has many types of operators, but the most common ones beginners use are:

1. Arithmetic Operators
2. Relational (Comparison) Operators
3. Logical Operators

We’ll discuss each in detail.

1️⃣ Arithmetic Operators

Used for mathematical calculations:

Example:

2️⃣ Relational Operators

Used to compare values. Result is 1 (true) or 0 (false).

Example: