Data Types

As the name suggests, data-type specifies the type of the data present in the variable. Variables must be declared with a data-type.

There are four different types of Data types in C.

Types	Data-type
Basic	int, char, float, double
Derived	array, pointer, structure, union
Enumeration	enum
Void	void

1. Basic data types

Basic data types are generally arithmetic types which are based on integer and float data types. They support both signed and unsigned values. Below are some of the oftenly used data types

Data type	Description	Range	Memory Size	Format specifier
int	used to store whole numbers	-2,147,483,648 to 2,147,483,647	4 bytes	%d
short int	used to store whole numbers	-32,768 to 32,767	2 bytes	%hd
long int	used to store whole numbers	-2,147,483,648 to 2,147,483,647	4 bytes	%li
float	used to store fractional numbers	6 to 7 decimal digits	4 bytes	%f
double	used to store fractional numbers	15 decimal digits	8 bytes	%lf
char	used to store a single character	-128 to 127 (signed) or 0 to 255 (unsigned)	1 byte	%c
unsigned char	used to store a single character	0 to 255	1 byte	%c
unsigned int	used to store positive whole numbers	0 to 4,294,967,295	4 bytes	%u
unsigned long	used to store positive whole numbers	0 to 4,294,967,295 (minimum)	4 or 8 bytes	%lu
long long int	used to store very large whole numbers	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807	8 bytes	%lld
unsigned long long	used to store very large positive numbers	0 to 18,446,744,073,709,551,615	8 bytes	%llu
_Bool or bool	used to store boolean values	0 or 1	1 byte	%d

Additional Data Types

size_t and ptrdiff_t

size_t: An unsigned integer type used to represent the size of objects in bytes and is guaranteed to be able to store the maximum size of any object. Format specifier: %zu
ptrdiff_t: A signed integer type used to represent the difference between two pointers. Format specifier: %td

Fixed-width Integer Types (from stdint.h)

C99 introduced fixed-width integer types that guarantee exact sizes across different platforms:

Data type	Description	Size	Format specifier
int8_t	Signed 8-bit integer	1 byte	%d (after casting) or use PRId8
uint8_t	Unsigned 8-bit integer	1 byte	%u (after casting) or use PRIu8
int16_t	Signed 16-bit integer	2 bytes	%d or use PRId16
uint16_t	Unsigned 16-bit integer	2 bytes	%u or use PRIu16
int32_t	Signed 32-bit integer	4 bytes	%d or use PRId32
uint32_t	Unsigned 32-bit integer	4 bytes	%u or use PRIu32
int64_t	Signed 64-bit integer	8 bytes	%lld or use PRId64
uint64_t	Unsigned 64-bit integer	8 bytes	%llu or use PRIu64

Examples

#include <stdio.h>
#include <float.h>
#include <stdbool.h>
#include <stdint.h>
#include <inttypes.h>

int main()
{
    // Basic types with proper sizeof usage (note: sizeof returns size_t)
    int x = 90;
    printf("size of int: %zu bytes\n", sizeof(int));
    printf("value of x: %d\n", x);
    
    // Unsigned types
    unsigned int ui = 4294967295U;
    printf("size of unsigned int: %zu bytes\n", sizeof(unsigned int));
    printf("max unsigned int: %u\n", ui);
    
    // Long long
    long long ll = 9223372036854775807LL;
    printf("size of long long: %zu bytes\n", sizeof(long long));
    printf("max long long: %lld\n", ll);
    
    // Float and double
    float f = 3.14f;
    printf("size of float: %zu bytes\n", sizeof(float));
    
    double d = 2.25507e-308;
    printf("size of double: %zu bytes\n", sizeof(double));
    
    // Character types
    char c = 'a';
    unsigned char uc = 255;
    printf("size of char: %zu byte\n", sizeof(char));
    printf("char value: %c, unsigned char value: %u\n", c, uc);
    
    // Boolean type
    bool flag = true;
    printf("size of bool: %zu byte\n", sizeof(bool));
    printf("bool value: %d\n", flag);
    
    // Fixed-width types
    int32_t fixed32 = 2147483647;
    uint64_t fixed64u = 18446744073709551615ULL;
    printf("int32_t value: %" PRId32 "\n", fixed32);
    printf("uint64_t value: %" PRIu64 "\n", fixed64u);
    
    // size_t and ptrdiff_t
    size_t size = sizeof(int);
    printf("size_t example: %zu\n", size);
    
    return 0;
}

Check result here

2. Derived Data types

Derived Data types are the ones which are derived from fundamental data types. Arrays, Pointers, Structures, etc. are examples of derived data types. Let's learn more about them in next chapters.

3. Enumeration Data types

Enumeration Data type is a user-defined data type in C. enum keyword is used to declare a new enumeration types in C.

Syntax

enum name{constant1, constant2, constant3, ....... };

Example

#include<stdio.h> 
  
enum month{January, February, March, April, May, June, July, August, September, October, November, December};
  
int main() 
{ 
    enum month name; 
    name = June; 
    printf("%d",name); 
    return 0; 
}

Check result here

4. Void Data types

Void specifies that there is no return value. Generally void is used in the below situations.

If the funtion has return type mentioned as Void, then it specifies that the function returns no value.
A function with out any parameters can accept void. For example., char greetings(void)
A pointer with type specified as void represents the address of an object but not it's type. Let's learn more about pointers in next chapters.