Unit 3: Fundamentals of C Programming | B. Sc Year: III

🧭 Introduction

After learning about programming languages in Unit 2, it’s time to start with an actual language—C programming.

C is one of the most important foundational programming languages, influencing languages like C++, Java, and Python. It is widely used for:

• Operating systems

• Embedded systems

• Compilers

• System software

This unit introduces the basic building blocks of C programming, essential for exams and for understanding later units.

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🔑 Key Concepts (Explained Clearly)

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1️⃣ What is C Programming Language?

C is a general-purpose, structured, procedural programming language developed by Dennis Ritchie (1970s) at Bell Labs.

Why C is important:

• Fast execution

• Close to hardware

• Portable (machine-independent)

• Used for system-level programming

C is often called the mother of programming languages.

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2️⃣ Structure of a C Program

A basic C program:

#include <stdio.h>

int main() {
    // Program statements
    return 0;
}

Parts of a C Program:

1. Preprocessor Directives – #include <stdio.h> tells compiler to include required files

2. main() Function – Entry point of execution

3. Statements – Instructions executed by the program

4. Return Statement – return 0; indicates successful execution

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3️⃣ Compilation and Execution

C programs run in two stages:

🛠 Compilation

• Converts C source code to machine code

• Checks syntax errors

• Produces executable file

▶ Execution

• OS loads the executable

• Program runs and produces output

Steps:

1. Preprocessing

2. Compilation

3. Linking

4. Execution

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4️⃣ C Character Set

Includes:

• Letters: A–Z, a–z

• Digits: 0–9

• Special Symbols: +, -, *, /, =, <, >, etc.

• Whitespace: space, tab, newline

These are used to form words, expressions, and statements.

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5️⃣ Tokens in C

Tokens = smallest units of a C program.

Types:

1. Keywords – Reserved words with special meaning

   int, float, if, else, return, for
   

2. Identifiers – User-defined names

   total, sum, calculate
   

3. Constants – Fixed values

   10, 3.14, 'A'
   

4. Operators – Symbols performing operations

   + - * / %
   

5. Punctuators – Symbols like

   ; , () {} []
   

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6️⃣ Keywords and Identifiers

✅ Keywords

• Predefined words in C

• Cannot be used as identifiers

• Example: int if while return

✅ Identifiers

• Programmer-defined names

• Rules:

  • Begin with letter or underscore

  • No spaces

  • Case-sensitive

Example:

int age;
float totalMarks;

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7️⃣ Variables and Constants

🔹 Variables

• Store data in memory

Declaration:

int num;

Declaration + Initialization:

int num = 10;

🔹 Constants

• Values that do not change

Using const:

const int max = 100;

Using #define:

#define PI 3.14

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8️⃣ Data Types in C

Basic Data Types:

Type	Example
int	5, 10
float	3.14
double	3.14159
char	'A'

Derived Data Types:

• Array

• Pointer

• Structure

• Union

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9️⃣ Expressions and Operators

An expression combines variables, constants, and operators.

int z = a + b * 2;

Operator Precedence (High → Low):

1. ()

2. * / %

3. + -

4. =

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🔟 Statements in C

Types:

1. Assignment Statement

x = 10;

2. Input/Output Statement

printf("Hello");
scanf("%d", &x);

3. Control Statement

if (x > 5) { ... }

4. Function Call

sqrt(25);

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1️⃣1️⃣ Comments in C

Make programs easy to understand.

Single-line:

// This is a comment

Multi-line:

/* This is
   a multi-line
   comment */

Ignored by compiler.

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1️⃣2️⃣ Escape Sequence Characters

Special characters for output formatting.

Escape	Meaning
\n	New line
\t	Tab
\\	Backslash
\"	Double quote

Example:

printf("Hello\nWorld");

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📝 Important Exam Questions

1. Define keywords and identifiers with examples

2. Explain structure of a C program

3. What are tokens in C?

4. Define variables and constants

5. Explain data types in C

6. What are escape sequence characters?

7. Explain expressions and operator precedence

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🧩 Step‑by‑Step Example

Program: Add Two Numbers

#include <stdio.h>

int main() {
    int a = 5, b = 3, sum;
    sum = a + b;
    printf("Sum = %d", sum);
    return 0;
}

Explanation:

• Variables declared

• Expression evaluated

• Result printed

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🎯 Exam Tips / Key Points

• Write program structure neatly

• Use examples for keywords & identifiers

• Write 3–4 points for theory answers

• Programs should have:

  • Header file

  • main() function

  • return 0;

• Commented programs get extra marks

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✅ Short Summary

Unit 3 covers the fundamentals of C programming, including:

• Structure of a C program

• Variables, constants, data types

• Tokens, keywords, identifiers

• Expressions, statements, comments

This unit forms the base for writing C programs, preparing you for input/output, operators, and control statements in later units.