C Basic

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;
}

Different between #include”Arun.c” and #include<Arun.c>

Syntax	Search Location	Usage	Example Case
#include "Arun.c"	First searches the current directory, then standard library paths	Use for files in your project folder	Your own source file or header in same directory
#include <Arun.c>	Searches only in standard library paths (compiler include directories)	Use for system/library files	Standard headers like <stdio.h> or library-provided files

Print the hello world using without semicolon ;

can print “Hello World” without using a semicolon by making use of control structures like if, while, or switch.
Here’s one simple example using if:

#include <stdio.h>

int main() {
    if (printf("Hello World")) {}  // printf returns the number of characters printed
}

How this works:

• printf() prints "Hello World" and returns the number of characters printed (which is non-zero here).
• The if statement doesn’t require a semicolon after the printf() because the if condition is inside parentheses.

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Another method using switch:

#include <stdio.h>

int main() {
    switch(printf("Hello World")) {}
}

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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

Const Variable:

If you declare a variable as const, you cannot modify it after initialization.

• const int x = 10; // x = 20; Error: assignment of read-only variable ‘x’
• The compiler enforces that the variable is read-only after being set.

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.

return:

• Function can return multiple statement?? Yes. If a function contains two return statements successively, the compiler will generate “Unreachable code” warnings.

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

Example: Format Specifier (float d=2.25;)

• printf(“%e,”, d); Here ‘%e’ specifies the “Scientific Notation” format. So, it prints the 2.25 as 2.250000e+000.
• printf(“%f,”, d); Here ‘%f’ specifies the “Decimal Floating Point” format. So, it prints the 2.25 as 2.250000.
• printf(“%g,”, d); Here ‘%g’ “Use the shorter of %e or %f”. So, it prints the 2.25 as 2.25.
• printf(“%lf,”, d); Here ‘%lf’ specifies the “Long Double” format. So, it prints the 2.25 as 2.250000.

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/

Find the fraction value using recursion

find a fraction value (e.g., 1/n) using recursion in C, you can recursively compute the numerator divided by the denominator instead of using an iterative or direct division.

Here’s an example:

Example: Recursively calculating 1/n

#include <stdio.h>

// Recursive function to calculate 1/n
double fraction(int n) {
    if (n == 1) // Base case: 1/1 = 1
        return 1.0;
    else
        return 1.0 / n + fraction(n - 1); // Recursion
}

int main() {
    int num;
    printf("Enter n: ");
    scanf("%d", &num);

    double result = fraction(num);
    printf("Sum of fractions 1 + 1/2 + ... + 1/%d = %lf\n", num, result);
    return 0;
}

Example run:

Enter n: 3
Sum of fractions 1 + 1/2 + ... + 1/3 = 1.833333

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finding just 1/n using recursion (without summing up), you can still do:

#include <stdio.h>

double reciprocal(int n) {
    if (n == 1)
        return 1.0;
    else if (n == 0) // Avoid divide by zero
        return 0.0;
    else
        return 1.0 / n;
}

int main() {
    int num = 4;
    printf("1/%d = %lf\n", num, reciprocal(num));
    return 0;
}

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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