Constant & Literal in C

C-Constant & Literal

Constant & Literal in C : 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 enumeration constants as well.
Constants are treated just like regular variables except that their values cannot be modified after their definition.

Integer Constant

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.

Rules for Constructing Integer Constants:

  1. An integer constant must have at least one digit.
  2. It must not have a decimal point.
  3. It can be either positive or negative.
  4. No commas or blanks are allowed within an integer constant.
  5. If no sign precedes an integer constant , it is assumed to be positive.

Here are some examples of integer literals −

212         /* Legal */
215u        /* Legal */
0xFeeL      /* Legal */
078         /* Illegal: 8 is not an octal digit */
032UU       /* Illegal: cannot repeat a suffix */

Character Constants

Character literals are enclosed in single quotes, e.g., ‘x’ 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 that represent special meaning when preceded by a backslash for example, newline (\n) or tab (\t).

Rules for Constructing Character constant:

  1. A character constant is a single alphabet, a single digit or a single special symbol enclosed within single inverted commas.
  2. The maximum length of a character constant can be 1 character

Following is the example to show a few escape sequence characters −

#include <stdio.h>

int main() {
   printf("Hello\tWorld\n\n");

   return 0;
}

Defining Constants

There are two simple ways in C to define constants −

  • Using #define preprocessor.
  • Using const keyword.

The #define Preprocessor

Given below is the form to use #define preprocessor to define a constant −

#define identifier value

Example:

#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;
}

When the above code is compiled and executed, it produces the following result −

value of area : 50

The const Keyword

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

const type variable = value;

The 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;
}

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