C

Variables

A variable is a container that holds data which can be changed during program execution.

1. Variable only start with alphabets or _ (underscore).
2. Variable in case-sensitive
3. Reserved keyword not allowed in variable name
4. Variable not start with digit
5. Variable should be meaningful
6. Special charactars not allowed in variable name

Data Type

📌 C Language Data Types

Data Type	Description	Size (Typical)	Format Specifier	Example
int	Integer (whole number)	2 or 4 bytes	%d	int a = 10;
short	Smaller integer	2 bytes	%hd	short b = 5;
long	Larger integer	4 or 8 bytes	%ld	long c = 100000;
long long	Very large integer	8 bytes	%lld	long long d = 1000000000LL;
unsigned int	Only positive integer	2 or 4 bytes	%u	unsigned int e = 25;
float	Single-precision floating number	4 bytes	%f	float f = 3.14f;
double	Double-precision floating number	8 bytes	%lf	double g = 3.14159;
long double	Extended precision floating number	10 or 12 bytes	%Lf	long double h = 2.718281828459;
char	Single character	1 byte	%c	char i = 'A';
unsigned char	0 to 255 character	1 byte	%c	unsigned char j = 'B';
signed char	-128 to 127 character	1 byte	%c	signed char k = 'C';
void	No value or empty type	—	—	void func();
pointer	Stores memory address of variable	4 or 8 bytes	%p	int *ptr = &a;

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✅ 1. Primary (Built-in) Data Types

Data Type	Keyword	Size (Typical)	Range / Description	Format Specifier	Example
Integer	int	2 or 4 bytes	-32,768 to 32,767 (2B) -2,147,483,648 to 2,147,483,647 (4B)	%d	10
Character	char	1 byte	-128 to 127 (signed) 0 to 255 (unsigned)	%c	'A'
Floating Point	float	4 bytes	~6 decimal digits precision	%f	3.14
Double	double	8 bytes	~15 decimal digits precision	%lf	3.1415926535
Void	void	0 bytes	No value / empty

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✅ 2. Type Modifiers

Modified Type	Keyword	Size (Typical)	Range	Format Specifier	Example
Short Integer	short int	2 bytes	-32,768 to 32,767	%hd	100
Long Integer	long int	4 or 8 bytes	-2,147,483,648 to 2,147,483,647	%ld	25000
Long Long Integer	long long int	8 bytes	-(2^63) to (2^63)-1	%lld	9876543210
Unsigned Integer	unsigned int	2 or 4 bytes	0 to 65,535 (2B) 0 to 4,294,967,295 (4B)	%u	50000
Unsigned Char	unsigned char	1 byte	0 to 255	%c	65
Long Double	long double	10/12 bytes	Higher precision than double	%Lf	3.14159L

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✅ 3. Derived Data Types

Data Type	Description	Example
Array	Collection of same data type	int a[5];
Pointer	Stores address of a variable	int *p;
Structure	Group of different datatypes	struct student { int id; char name[20]; };
Union	Shared memory storage for different data types	union data { int x; float y; };
Enum	User-defined constants list	enum week {Mon, Tue, Wed};
Function	Block of reusable code	int add(int a, int b);

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✅ 4. Boolean Support in C (via <stdbool.h>)

Type	Keyword	Size	Value	Example
Boolean	bool	1 byte	true / false	bool isReady = true;

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🔔 Note: Size of data types may vary on compiler and architecture (32-bit vs 64-bit).