Introduction to C Programming

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Introduction to C Programming

C is a general-purpose, procedural programming language widely used for system software,

embedded systems, operating systems, compilers, and application development. It is also an

excellent language for learning fundamental programming concepts such as variables, memory,

pointers, functions, and data structures.

1. History of C

The C programming language was developed by Dennis Ritchie at Bell Laboratories in the early

1970s.

Evolution

A simplified history is:

BCPL → B → C → C++ / Java / C# and many other languages

C was initially developed for the development of the UNIX operating system.

Important points

Developed by Dennis Ritchie

Developed at Bell Laboratories

Created around 1972

Originally used to develop UNIX

Standardized by ANSI in 1989 as ANSI C

Later standardized by ISO

Why is C still important?

Many modern programming languages have concepts that originated from or are strongly influenced by C.

For example:

int age = 20;

The concepts of variables, data types, operators, functions, arrays, and pointers are fundamental to

many programming languages.

2. Features of C

C has several important features.

1. Simple

C has a relatively small set of keywords and a simple syntax.

int a = 10;

int b = 20;

int sum = a + b;

2. Procedural

C follows a procedure-oriented programming approach.

A program can be divided into functions.

void display(){

printf("Hello");

}

3. Portable

C programs can generally be moved between different platforms with relatively few changes.

For example, the same C source code can potentially be compiled on:

Windows

Linux

macOS

Embedded systems

4. Fast and Efficient

C provides low-level memory access and generally produces efficient machine code.

5. Structured

Large programs can be divided into smaller functions.

int add(int a, int b){

return a + b;

}

6. Rich Set of Operators

C provides operators such as:

+ - * / %

> < == !=

&& || !

& | ^ << >>

7. Supports Pointers

Pointers allow a program to work directly with memory addresses.

int x = 10;

int *ptr = &x;

8. Extensible

C programs can be extended by creating user-defined functions and using libraries.

3. Structure of a C Program

A basic C program generally contains:

Preprocessor directives

Functions

main() function

Statements

Comments

Example:

#include <stdio.h>

int main(){

printf("Hello World");

return 0;

}

Explanation

#include

Includes the standard input/output library.

int main()

The main() function is the starting point of program execution.

printf("Hello World");

Displays output on the screen.

return 0;

Indicates successful program termination.

4. Compilation and Execution Process

A C program is not directly executed by the computer. It goes through several stages.

Process

C Source Code

↓

Preprocessor

↓

Compiler

↓

Assembler

↓

Linker

↓

Executable File

↓

Execution

Suppose we have:

#include <stdio.h>

int main(){

printf("Hello");

return 0;

}

Step 1: Source Code

The programmer writes the program in a .c file.

hello.c

Step 2: Preprocessing

Preprocessor directives such as:

#include

are processed.

Step 3: Compilation

The compiler checks the C code and converts it into assembly-level code.

Step 4: Assembly

The assembler converts assembly code into machine/object code.

Step 5: Linking

The linker combines the object code with required library code.

For example, the implementation of printf() comes from the standard library.

Step 6: Execution

The final executable program is loaded and executed.

5. Basic C Program

Example:

#include <stdio.h>

int main(){

int a = 10;

int b = 20;

int sum;

sum = a + b;

printf("Sum = %d", sum);

return 0;

}

Output

Sum = 30

Program breakdown

Part Purpose

#include Includes standard I/O functions

main() Starting point

int a = 10 Declares integer variable

sum = a + b Performs addition

printf() Displays result

return 0 Terminates program

6. Tokens in C

A token is the smallest meaningful unit of a C program.

C tokens are broadly classified into:

Keywords

Identifiers

Constants

String literals

Operators

Special symbols

Example:

int sum = a + 10;

Tokens include:

int

sum

;

7. Keywords

Keywords are reserved words that have a predefined meaning in C.

Examples:

int

float

char

double

else

for

while

return

void

struct

switch

case

break

continue

Example:

int age = 20;

Here:

int → keyword

age → identifier

20 → constant

= → operator

; → special symbol

You cannot use a keyword as a variable name.

Incorrect:

int int = 10;

8. Identifiers

Identifiers are names given to programming elements such as:

Variables

Functions

Arrays

Structures

Example:

int studentAge = 20;

Here:

studentAge

is an identifier.

Rules for identifiers

Can contain letters, digits and underscore.

Cannot start with a digit.

Cannot contain spaces.

Cannot be a keyword.

C is case-sensitive.

Valid:

age

studentAge

student_1

totalMarks

Invalid:

1student

student age

float

total-marks

9. Variables

A variable is a named memory location used to store data.

Example:

int age = 20;

Here:

int → data type

age → variable name

20 → initial value

Another example:

float salary = 25000.50;

char grade = 'A';

Declaration

int age;

Initialization

age = 20;

Or both together:

int age = 20;

10. Constants

A constant is a value that does not change during program execution.

Examples:

3.14

'A'

"Hello"

Using const

const float PI = 3.14159;

Now attempting to change PI is not allowed.

PI = 4.5; // Error

Using #define

#define PI 3.14159

Example:

#include

#define PI 3.14159

int main(){

printf("PI = %f", PI);

return 0;

}

11. Data Types in C

A data type tells the compiler what kind of data a variable can store.

Common C data types include:

char

int

float

double

void

C also supports derived types such as:

arrays

pointers

functions

and user-defined types such as:

struct

union

enum

typedef

Basic data types

Data Type Typical Purpose

char Character

int Integer

float Single-precision decimal

double Double-precision decimal

void No value

Example:

char grade = 'A';

int age = 20;

float price = 99.50f;

double distance = 12345.6789;

The exact size of C data types is implementation-dependent, so use sizeof() when you need

to know the size on a particular system.

Example:

printf("%zu", sizeof(int));

12. Pointers as a Derived Data Type

A pointer is a variable that stores the memory address of another object.

Example:

int number = 10;

int *ptr = &number;

Here:

number → stores 10

ptr → stores the address of number

Example

#include <stdio.h>

int main(){

int number = 10;

int *ptr = &number;

printf("Value = %d\n", number);

printf("Address = %p\n", (void *)ptr);

printf("Value using pointer = %d\n", *ptr);

return 0;

}

Output may look like:

Value = 10

Address = 0x7ffe1234

Value using pointer = 10

&number means address of number.

*ptr means value stored at the address contained in ptr.

13. Basic Input and Output

C commonly uses functions from for input and output.

Output using printf()

#include <stdio.h>

int main(){

printf("Hello World");

return 0;

}

Formatting values

int age = 20;

printf("Age = %d", age);

Common format specifiers:

Specifier Used for

%d Integer

%f Floating-point

%c Character

%s String

%lf double in scanf()

%p Pointer address

14. Input using scanf()

Example:

#include <stdio.h>

int main(){

int age;

printf("Enter your age: ");

scanf("%d", &age);

printf("Your age is %d", age);

return 0;

}

Suppose the user enters:

Output:

Your age is 20

Notice:

scanf("%d", &age);

The & gives the address of age, allowing scanf() to store the entered value there.

15. Character Input

#include <stdio.h>

int main(){

char grade;

printf("Enter grade: ");

scanf(" %c", &grade);

printf("Grade = %c", grade);

return 0;

}

The space before %c:

" %c"

helps scanf() skip whitespace left in the input stream.

< Pointers in c Pointer Arithmetic in C >

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