Starting with C programming offers great opportunities! Let’s kick things off with a brief overview of the basics to get you started:

Remember, mastering programming requires time and practice, so don’t get discouraged if you face difficulties along the way. Keep coding and experimenting, and you’ll improve over time!

Read more: C – Basic

Get start

1. Setup your environment: You need a compiler to write and run C programs. Popular choices include GCC (GNU Compiler Collection), Clang, and Visual Studio for Windows. Install one based on your operating system.
2. Choose a text editor or IDE: You can write C code in any text editor, but using an Integrated Development Environment (IDE) can make your life easier. Some popular options include Visual Studio Code, Atom, Sublime Text, and Eclipse.
3. Learn the basics: Familiarize yourself with basic C syntax, such as variables, data types, operators, loops (like for and while loops), conditional statements (if-else), functions, arrays, and pointers. These are the building blocks of any C program.
4. Compile and run: Save your program with a “.c” extension (e.g., hello.c). Open a terminal or command prompt, navigate to the directory containing your program, and compile it using the compiler you installed. For GCC, the command would be: gcc hello.c -o hello This command compiles your code into an executable named “hello”. Then, run the executable: ./hello You should see “Hello, World!” printed to the screen.
5. Practice: Once you’ve got the basics down, practice writing more complex programs. Try solving small programming challenges or work on projects that interest you.
6. Learn from resources: There are plenty of online resources, tutorials, and books available to help you learn C programming. Websites like GeeksforGeeks, Tutorialspoint, and the C programming subreddit can be valuable learning resources.
7. Debugging: Learn how to debug your programs when something goes wrong. Understanding concepts like breakpoints, stepping through code, and reading error messages will be immensely helpful.
8. Explore more advanced topics: Once you’re comfortable with the basics, you can delve into more advanced topics like memory management, file handling, data structures, and algorithms.

Write your first program

A classic first program is the “Hello, World!” program. It simply prints “Hello, World!” to the screen. Here’s how you can write it:

#include <stdio.h>

int main() {
    printf("Arun E, World!\n");
    return 0;
}

Join a community

Participating in online forums or joining a local programming group can provide support, encouragement, and opportunities to learn from others.

Constants

• (Two types : Primary, Secondary)
• When the program execution time constants should not change their value (A constant is an entity that doesn’t change)

Constant Type	Constant Sub Type	Type	Type	Description	Example
Primary Constant	Numeric Constant (Three Type)	Integer	Decimal	Decimal constants are 0 to 9 numbers	86 , 94 , -133
Primary Constant	Numeric Constant (Three Type)	Integer	Octal	Octal constants are 0 to 7 numbers. First number should be ‘0‘	0137 , -0567 , 034
Primary Constant	Numeric Constant (Three Type)	Integer	Hexadecimal	Hexadecimal constants are 0 to 9 and A to F. First number should be start with ‘0x’ or ‘0X’	0X73A , 0x89FA
Primary Constant	Real or floating point Constant (Two types)	Fractional form	Fractional form	dot points are consider as fractional forms	-0.567 , .64 , 24.0
Primary Constant	Real or floating point Constant (Two types)	Exponential form	Exponential form	Rules: May use mantissa and exponent symbols Should not use .dot point in exponent Should have at-least one digit in exponent	0.2571e-5, mantissa – 0.2571, exponent – -5
Primary Constant	Character Constant	Character Constant	Character Constant	Character constant are come with two single quotes (‘)	‘A’ – (ASCII-65) ‘O’ – (ASCII-48, EBCDIC-240) ‘a’ – (ASCII-97, EBCDIC-129) ‘z’ – (ASCII-122, EBCDIC-269) % – (ASCII-37, EBCDIC-108)
Primary Constant	String constant	String constant	String constant	String constant are come with two double quotes (“)	“ARUN” – Valid “2020” – Valid “A” – Valid “ABC – Invalid ‘sum’ – Invalid
Secondary Constant	Array
Secondary Constant	Pointer
Secondary Constant	structure
Secondary Constant	union
Secondary Constant	enum

Floating Points

• floating points may contain . dot point.
• Rule-1: Should use 0 to 9 numbers.
• Rule-2: Dot point may come front or back
• Rule-3: In the case of float numbers, place sign symbols in front of them.
• Example : 537.36, -158.77

How does the system store a negative integer?

• Usually, all the negative integers are store in computers in the form of the two’s complement of the same positive integer.
• Eg: 1011 (-5) Step-1 − One’s complement of 5: 1010, Step-2 − Add 1 to above, giving 1011, which is -5.

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Character Set

Type	character set
Alphabets	A, B, …. Y, Z a, b, …. y, z
Digits	0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Special symbols	~ `! @ # $ % ^ & * ( ) _ - + = | \ { } [ ] : ; ” ’ < > , . ? /
White space	Blank space, Horizontal tab, Carriage return, New line , Form feed.

Reserved Keywords

C89 Reserved Keywords

According to C89 standards c has 32 reserved keywords

auto	do	goto	signed	unsigned
break	double	if	sizeof	void
case	else	int	static	volatile
char	enum	long	struct	while
const	extern	register	switch
continue	float	return	typedef
default	for	short	union

Enum:

• Enumeration (or enum) represents a user-defined data type in C. It primarily assigns names to integral constants, making programs easier to read and maintain
• --  or ++  are can’t be done on enum value.

C99 Reserved Keywords

According to C99, C has 5 more reserved keywords

• _Bool
• _Complex
• _Imaginary
• inline
• restrict

C11 Reserved Keywords,

According to C11, C has 7 more reserved keywords

• _Alignas
• _Alignof
• _Atomic
• _Generic
• _Noreturn
• _Static_assert
• _Thread_local

Identifiers

Rules

• Should not use keyword as a identifier.
• First letter should be English word.
• May use Uppercase and Lowercase letters.
• Can use _ underscore as a first letter of Identifier.
• Identifiers are case sensitive(below both identifiers are not same)

Example

• Valid Identifiers: Sum, basic_pay, a1, Ab, ab.
• Invalid Identifiers: 8a – First letter should not be numbers, auto – auto is a keyword

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Variables

• When the program execution time variable may be change their value.(A variable is an entity that does change),
• Example: Sum , average , basic_pay , basic-pay , A0 etc (valid variables)
• Generally variables are store in different storage class types : automatic , static , extern , register

Declaring a variable

Rules

• should be declared data type of variable.
• data types name should be declared data type’s
• if declare multiple variables in a single data type, separate each by, operator
• Every declaration should end with ; semicolon

Syntax

• datatype variable_1, variable_2, …..variable_n ;
• Example-1: int a, b , c; //here a,b, c are integer variables
• Example-2: float salary; //here salary is a floating type variable.

Use of variable declaration

• Compiler can allocate a memory when we declared data type variable

Variable Initializing

• Syntax: datatype variable_name = initial value;
• Example: int sum = 1;

Assigning Value to Variable

Assigning Operator = equal is used to assign value to variable in

• Syntax for value : Variable_name = value; Ex: x = 20;
• Syntax for another variable: variable_name = variable; Ex: y = x;
• Syntax for expressions: variable_name = expression; Ex: z = x+y;

Exercise

Q : Which of the following is not a valid variable name in C?
A. 1 a @
B. a 1 2
C. a b 123
D. a b c 123

Answer: Option A (Explanation: First character must be alphabet).

You cannot print (automagically) the type of a variable in C. Variables and their types are only known at compile time.

At runtime, there is no variables (only locations & values) and almost no types:

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Data types

• Data types in any of the language means that what are the various type of data the variables can have in that particular language.
• Whenever a variable is declared it becomes necessary to define data type that what will be the type of data that variable can hold.
• basic datatype: char , int , float and double.
• type modifier (Qualifier) : short , long , signed and unsigned
• Rules : Every variable should have any one of the following data type

Types	bit Size	Byte Size	Range
char (or) signed char	8	1	127 to 127
unsigned char	8	1	0 to 255
int (or) signed int	16	2	-32,767 to 32,767
unsigned int	16	2	0 to 65,535
short int (or) signed short int	8	1	-127 to 127
unsigned short int	8	1	0 to 255
long int (or) signed long int	32	4	-2,147,483,647 to 2,147,483,647
unsigned long int	32	4	0 to 4,294,967,295
float	32	4	3.4E-38 to 3.4E+38
double	64	8	1.7E-308 to 1.7E+308
long double	80	10	3.4E-4932 to 1.1E+4932
unsigned sort	16	2

The various general types of data are:

General type	General Sub type	Data Type
Number type data	Integer Type	int
Number type data	Float type (Three Types)	Float
Number type data	Float type (Three Types)	double
Number type data	Float type (Three Types)	long double
Character type data		char
String type data
Boolean type data		bool

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C Programming Structure

• Pr-processor Commands
• Type definition
• Function prototype – Declare function type and variable passed to functions
• Variable – We must have a main function in every c programs

//pre processor command
#include <stdio.h>

//variable type definition ("a" is a variable and integer type)
int a; 

//Function prototype ("Func" is a integer type function name with arguments "a", "b" is a variables integer type)
int Func(int b, int c); 

//main function integer type
int main()
{
	//"E" Local variable integer type
    int E;
	
    C statements;
}


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Hello World C program

Code

#include<stdio.h>

void main()
{
 
   printf("ArunEworld");
}

Output : ArunEworld

Note : All the programs are run in gnu gcc of linux.

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Escape sequence

Escape sequence is a character constant or string constants, its a non graphical character or printable.

Escape sequence	Example
\a  – alarm character
\b  – back space
\f  – form feed
\n  – new line
\r  – carriage return Carriage return is known as cartridge return and often shortened to CR, <CR> or return. It is a control character or mechanism used to reset a device position to the beginning of a line of text. It is closed associate with the line feed and newline concepts.
\t  – horizontal tab
\v  – vertical tab
\\  – back slash
\?  – question mark
\’  – single quote
\”  – double quote
\000  – character representation \xbh – character representation
\0  – nul character Difference between ‘/0’  and ‘\0’  in C programming?‘\0’ – Null terminator in array.

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Header files (Two types)

Predefined Header files

• Syntax : #include<file_name> (Stored in Specified directories).
• If a header file is included with in < > then the compiler searches for the particular header file only with in the built in include path.

User defined Header files

• Syntax : #include “file_name” (Stored in Locally saved programs).
• If a header file is included with in “ “ , then the compiler searches for the particular header file first in the current working directory, if not found then in the built in include path.

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Command Statements

• /* Commands */ – Commands in paragraph
• // commands – command in single line

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Format specifier

Specifier	Description
%i	Can be used to input integer in all the supported format.
%c	single character
%d	decimal character
%e	floating point value
%f	floating point value
%g	floating point value
%h	short integer
%ld	long integer
%o	octal integer
%s	string
%u	unsigned decimal integer
%x	hexa decimal integer
%p	print the address of the variable
[...]	string which may include white spaces

Little Endian & Big Endian

• Explanation: https://aruneworld.com/embedded/little-endian-and-big-endian/
• Code Example: https://aruneworld.com/programming-language/c/c-examples/c-example-little-endian-and-big-endian/

Next Topic

C – Basic

C – Operator

C – Decision making, Branching, Looping

C – Functions

C – Storage Class

C – Extern

C – Array

C – Pointer

C – Memory Allocation

C – Structure

C – Union

C – Structure and Union

C – Macros

C – Preprocessor and Macros

C – File Management

C – Coding Standard

C – Compilers

C – Compiling Process

C File Management

C Library

C Example

File management in the C programming language involves operations related to reading from and writing to files. Here are some key concepts and functions for file management in C:

File Pointers

• C uses a file pointer to keep track of the current position in a file.
• FILE is a structure in C that represents a file stream. You declare a pointer to this structure to work with files.
• Syntax: FILE *filePointer;

File Functions in C

Function	Note	Syntax
Fopen()	Open a new file or open an existing file.	FILE *fopen( const char * filename, const char * mode );
fclose()	close a file.	int fclose( FILE *fp);
fputc()	Writing a file.	int fputc( int c, FILE *fp );
fgetc()	Reading a file.	int fgetc( FILE * fp );

Opening a File: Fopen() Function

Syntax: fopen(“file_name”,"mode”);

File Modes: generic file handling

• r – Open an existing file for Read purpose
• w – Open an existing file for Write purpose
• a – Open a file for writing in append mode. If file not exist, then create new file.
• r+ – Open a file for both Read and Write
• w+ – Opens a file for Read and Write. If a file is not existing it creates one, else if the file is existing it will be over written.
• a+ –

Closing a File: fclose() Function

• After using a file, it’s important to close it using the fclose function.
• Syntax: fclose(filePointer);

Reading from a File

• For reading from a file, you use functions like fscanf, fgets, or fread.
• Syntax: fscanf(filePointer, "%s", buffer); // Read a string

Writing to a File:

• For writing to a file, you use functions like fprintf, fputs, or fwrite.
• Syntax: fprintf(filePointer, "Hello, World!\n");

Error Handling:

• It’s important to check if file operations are successful. The functions usually return NULL on failure.
• Syntax: if (filePointer == NULL) { // Handle error }

File Positioning:

• fseek and ftell functions can be used to set the file position indicator and get the current position.

Syntax:

fseek(filePointer, 0, SEEK_SET); // Move to the beginning of the file long position = ftell(filePointer); // Get the current position

Removing a File:

• The remove function can be used to delete a file.
• Syntax: remove("example.txt");

These are basic file management operations in C. Remember to always handle errors and close files after using them to avoid data corruption or loss.

NEXT

C – Basic

C – Operator

C – Decision making, Branching, Looping

C – Functions

C – Storage Class

C – Extern

C – Array

C – Pointer

C – Memory Allocation

C – Structure

C – Union

C – Structure and Union

C – Macros

C – Preprocessor and Macros

C – File Management

C – Coding Standard

C – Compilers

C – Compiling Process

C File Management

C Library

C Example

Storage classes in C determine a variable’s scope, visibility, lifetime, and storage location. They include auto, extern, static, and register. The default initial value varies based on the storage class. Scope defines variable visibility, while lifetime dictates its persistence in memory.

Read more: C – Storage Classes

• Scope: The extent to which different parts of a program have access to the variable, determining its visibility.
• Lifetime refers to the duration for which the variable persists in memory, encompassing the allocation and deallocation of its storage. The scope also influences a variable’s lifetime.
• variable types(Global variable)

Variable Type	Lifetime	Scope
Global Variable	Only destroyed when the program terminates	Only the program
Local Variable	Allocated memory when entering the function, destroyed when leaving	Limited to the function

• syntax: storage_class_specifier data_type variable_name;

Specifiers	Lifetime	Scope	Default Initialize
auto	Block (inside function)	Block	Uninitialized
register	Block (stack or CPU register)	Block	Uninitialized
static	Program	Block or compilation unit	Zero
extern	Program	Block or compilation unit	Zero
(none)	Dynamic (heap)	nil	Uninitialized

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Auto Keyword

A variable declared inside a function without any specified storage class is termed an auto variable.

• Only usable within functions.
• Created and destroyed automatically upon function call and exit, respectively.
• Compiler assigns them garbage values by default.
• The stack memory stores local variables.
• By default, every local variable in a function is of auto storage class.

Example:

void f() {
    int i;    // auto variable
    auto int j;   // auto variable
}

Global variable

• A variable declared outside any function is a global variable.
• Any function in the program can change its value.
• initializing
  • int – 0
  • char – \0
  • float – 0
  • double -0
  • pointer – null

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Register Keyword

The “register” keyword specifies that local variables are stored in a register for rapid access, particularly for counters. These variables offer quicker access than normal ones, but only a limited number can be placed in registers. While the compiler sees “register” as a suggestion, it ultimately decides. Typically, compilers optimize and determine variable allocation.

Register Note 1:

Attempting to access the address of a register variable results in a compile error. For instance:

int main() {
    register int i = 10;
    int *a = &i; // Compile error
    printf("%d", *a);
    getchar();
    return 0;
}

Register Note 2:

You can use the register keyword with pointer variables. Below is a valid example:

int main() {
    int i = 10;
    register int *a = &i;
    printf("%d", *a); // Output: 10
    getchar();
    return 0;
}

Resistor Note 3:

Register is a storage class, and C prohibits multiple storage class specifiers for a variable. Therefore, you cannot use register with static.

int main() {
    int i = 10;
    register static int *a = &i; // Error
    printf("%d", *a);
    getchar();
    return 0;
}

Register Note 4:

There’s no limit to the number of register variables in a C program. However, the compiler may choose to allocate some variables to registers and others not.

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static keyword

• static means its take only single or same memory.
• static is initialized only once and remains into existence till the end of program
• static assigned 0 (zero) as default value by the compiler.
• A static local variables retains its value between the function call and the default value is 0.
• If a global variable is static then its visibility is limited to the same source code.
• Static variables stored in Heap(Not in Stack memory)
• The following function will print 1 2 3 if called thrice.
• Example
  • void f() { static int i; ++i; printf(“%d “,i); }

• In “static int a[20];”, variable “a” is declared as an integer type and static. When a variable is declared as static, it is automatically initialized to the value ‘0’ (zero).

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What is a static function?

• A function prefixed with the static keyword is called a static function.
• You would make a function static if it should only be called within the same source code or be visible to other functions in the same file.
• static has different meanings in in different contexts.
• When specified on a function declaration, it makes the function local to the file.
• When specified with a variable inside a function, it allows the vairable to retain its value between calls to the function

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storage class specifier

• typedef – typedef is the storage class specifier.
  • It does not reserve the storage.
  • It is used to alias the existing type. Also used to simplify the complex declaration of the type.
• reference links
  • https://en.wikipedia.org/wiki/C_syntax

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volatile

• The compiler omits optimization for objects declared as volatile because code outside the current scope can change their values at any time.

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Advantages and Disadvantages

Storage Class	Advantage	Disadvantage
auto	Automatically allocated and deallocated within functions	Garbage values if not explicitly initialized
register	Faster access due to storage in CPU registers	Limited availability of register space; Compiler-dependent
static	Persistent value across function calls	Global scope may lead to namespace pollution; May increase memory usage
extern	Allows sharing of variables across multiple files	Global scope may lead to namespace pollution

Interview Questions

What are storage classes in ‘C’ language?

• automatic class
• static class

How many storage class specifiers in “C” language?

• auto,
• register,
• static
• extern

How many variables scopes are there in “C” language?

• Body.
• Function.
• Program.
• File.

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NEXT

In C programming, functions are essential building blocks for organizing and reusing code.

• Rule: In C, you cannot define a function inside another function.
• Rule: But you can call a function inside another function.
• Rule: Functions cannot return more than one value at a time because, after returning a value, control is passed back to the calling function.
• Any function, including main(), can call itself recursively.
• C has two kinds of functions User Defined Functions,  Pr-Defined Libarary Functions.

Read more… →