C Constants and Literals

 5    C Constants and Literals

The constants refer to fixed values that the program may not alter during its execution.

 These fixed values are also called literals.

 Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.

The constants are treated just like regular variables except that their values cannot be modified after their definition. 

Integer literals 

An integer literal can be a decimal, octal, or hexadecimal constant.

A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal.

 An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. 

The suffix can be uppercase or lowercase and can be in any order. Here are some examples of integer literals

Floating-point literals

 A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part.

 You can represent floating point literals either in decimal form or exponential form. 

While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form, you must include the integer part, the fractional part, or both.

 The signed exponent is introduced by e or E. 

Character constants 

Character literals are enclosed in single quotes, 

e.g., 'x' and can be stored in a simple variable of char type.

 A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'),

 or a universal character (e.g., '\u02C0').

There are certain characters in C when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). 

String literals

 String literals or constants are enclosed in double quotes "". 

A string contains characters that are similar to character literals: 

• plain characters,
•  escape sequences
• universal characters. 

You can break a long line into multiple lines using string literals and separating them using whitespaces. Here are some examples of string literals. 

All the three forms are identical strings

Defining Constants 

There are two simple ways in C to define constants: 

1. Using #define preprocessor. 

2. Using const keyword. 

The #define Preprocessor Following is the form to use #define preprocessor to define a constant:

#define identifier value

eg:

#include <stdio.h>

#define LENGTH 10 

#define WIDTH 5 

#define NEWLINE '\n' 

int main() 

{

     int area; 

     area = LENGTH * WIDTH;

     printf("value of area : %d", area); 

     printf("%c", NEWLINE); 

     return 0;

 } 

The const Keyword 

You can use const prefix to declare constants with a specific type as follows: 

const type variable = value; 

Following example explains it in detail: 

#include <stdio.h>

int main() 

{ 

     const int LENGTH = 10;

     const int WIDTH = 5; 

     const char NEWLINE = '\n';

     int area; area = LENGTH * WIDTH; 

     printf("value of area : %d", area); 

     printf("%c", NEWLINE);

     return 0;

}