What is constant  in C programming? In the previous tutorial on C programming, we learned what is Variable? Today in this tutorial, we will learn what is constant  in C programming? What is constant  in C?

What is constant  in C programming?

Constant  is also a normal variable but its value does not change during the execution of the program.  that refers to constant  fixed value in programming which means once the execution of the program is defined. Its value cannot be changed during Fixed value is called literal.

If a constant 's value is tried to change during the execution 

of the program, a compilation error is found.

Constant  when and why define?
 

This question definitely arises in the mind of almost every new programmer, why should we use constant  instead of using simple variable? As I said above, constant  is same as simple variable but its value does not change during execution of program.

We use Constant  when we have to fix a value whose value never changes such that the value of pie is 3.14 which is always fixed.

C programming is the base of all programming language, so it is also called mother language. When we create a program on the basis of class and object in programming, we can easily use it in all the functions by defining constant  in one place, whereas the object or this keyword has to be used to use the variable in another function. Which is a slight alter, so we use constant .

Constant 's value does not change during the execution of the program, so constant  does not need to be reloaded in memory repeatedly.

types of C Constant

• Integer Constant
• Floating point constant
• String constant
• Character constant

Integer constant 

Integer constant  has values ​​stores of integer type such as 5, 7, 8. Integer constant  can contain decimal, octal and Hexadecimal literals. Prefix specifies base and radix. Such as 0x and 0X represent Hexadecimal, 0 Octal and if any prefix character is not preceded by any number, it represents decimal.

The suffix (end) of Integer literals can also have U or L in it, where U represents unsigned while L represents long. Suffix (U or L) can be upper case and lower case in any case.

Some examples of different types of integer literals

345 /** Decimal **/

0520 /** Octal **/

0x365a /** Hexadecimal **/

604 /** Int **/

604u /** unsigned int **/

42l /** long**/

42ul /** unsigned long **/

Floating point constant 

Floating point constant  consists of value stores of floating type, meaning value stores of decimal type. Floating point literals have decimal part, integer part, fractional part and exponent part. You can represent floating point literals in decimal part and exponential part.

When you represent a decimal form, it must be a decimal part or exponent part or both. And when representing the exponential form, it must be either integer part or fractional part or both. Signed exponent is introduced by e and e.

Some examples of floating point literals:

3.1414      /** legal **/

314159E-5L    /**legal**/

403E          /* Illegal: incomplete exponent */

220f          /* Illegal: no decimal or exponent */

.e75          /* Illegal: missing integer or fraction */

Character Constant 

Character constant  stores a single character. Character literals are enclosed in single quotes such as 'a', 'y'. Character literals can be plain character (e.g., 'a'), escape sequence (e.g., '\ n') or universal character (e.g., '\ u02C0').

There are many characters in C programming whose prefixed backslash (\) creates their special meaning like \ n = new line, \ t = tab,

Here are the list of escape sequence.

Escape Sequence	Meaning
\\	\ character
\'	' character
\"	" character
\a	Alert or bell
\b	Backspace
\f	Form feed
\n	Newline
\r	Carriage return
\t	Horizontal tab
\v	Vertical tab
\?	? character
\ooo	Octal number of one to three digits
\xhh...	Hexadecimal number of one or more digits

String constant 

String constant  has value stores of string type. String literals (string type values) are enclosed in double quotes. String literals can have one or more character combinations. It also has plain characters, escape sequences and universal characters store as character constant .

The null character (\ 0) at the end of the string is automatically created by the compiler.

const char a[4] = "wait";

define constant  in C?

In C programming, constant  can be defined in two ways.

• #define using preprocessor directive

• using const keyword

Let us now learn how to define constant  in the program using both methods.

# how to define constant  via define preprocessor directive?

The source code is processed by a program called preprocessor before the C program compile in the compiler. Here we can define constant  using #define.

Syntax:

#define identifierName value

Here identifierName means meaningful constant  name and value means that value which will be assigned to that constant .

The below given program explains how to define constant  in C programming using #define preprocessor.

#include

#define FIRSTNUMBER 5420

#define SECONDNUMBER 430.2

#define CHARVALUE 'A'

#define STRVALUE "Hello"

int main()

{

    printf("Integer Constant : %d\n",FIRSTNUMBER);

    printf("Floating point Constant : %f\n",SECONDNUMBER);

    printf("Character Constant : %c\n",CHARVALUE);

    printf("String Constant : %s\n",STRVALUE);

    return 0;

}

Live Demo

Output of the above program

Integer Constant : 5420

Floating point Constant : 430.200000

Character Constant : A

String Constant : Hello

How to define constant  in C programming using const keyword?

The const keyword is a pre-defined word that is reserved for the system. If const keyword is written before any simple variable, then that variable becomes constant . like :

Syntax:-

const datatype variableName value;

defining constant  using const keyword

In the given program, the process of constant  defining using const keyword has been described.

#include

int main()

{

    const int FIRSTNUMBER = 5420;

    const float SECONDNUMBER =  430.2;

    const char CHARVALUE = 'A';

    const char STRVALUE[5] = "Hello";

    printf("Integer Constant : %d\n",FIRSTNUMBER);

    printf("Floating point Constant : %f\n",SECONDNUMBER);

    printf("Character Constant : %c\n",CHARVALUE);

    printf("String Constant : %s\n",STRVALUE);

    return 0;

}

Live Demo

Output of the above program

Integer Constant : 5420

Floating point Constant : 430.200012

Character Constant : A

String Constant : Hello

It is a good programming practice that always write constant  name in capital letter.

Read also :-

•  Operators in c programming

• C / C ++ Programming language tutorial