C Constants

In this tutorial, you will learn about C constants and how to create them in C Programming.


Constants are the same as variables except they cannot be changed once defined.

C constants are one of the most fundamental and essential parts of the C programming language. Constants in C are the same as variables but the values are fixed, and its value remains the same during the entire execution of the program.

  • Constants can be any of the data types.
  • Constants are also called literals.
  • The best practice in C language is to define constants in upper-case characters.

Defining a C constant

There are two ways to define a constant in the C language.

  1. const keyword
  2. #define preprocessor

1) Defining C constant using const keyword

Syntax

const type constant_name;

Example

#include<stdio.h> 
int main(){ 
const float PI=3.14; 
printf("The value of PI is: %f",PI); 
return 0; 
}

Program output

The value of PI is: 3.140000

Putting const either before or after the data type is possible.

const float PI = 3.14;

or

float const PI = 3.14;

If you try to change the value of PI, it will give the compile-time error.

#include<stdio.h> 
int main(){ 
const float PI=3.14; 
PI=4.5; 
printf("The value of PI is: %f",PI); 
return 0; 
}

Program output

Compile Time Error: Cannot modify a const object

2) Defining C constant using #define preprocessor

The #define preprocessor is also used to define constant. We will learn about the #define preprocessor directive in the later chapter.

Types of C constant

Constant Example
Integer Constant 10, 20, 30, 250 etc.
Real or Floating-point Constant 11.5, 22.4, 250.3 etc.
Octal Constant 036, 012, 045 etc.
Hexadecimal Constant 0x3a, 0x5b, 0xbb etc.
Character Constant ‘a’, ‘b’, ‘x’ etc.
String Constant “c”, “c tutorial”, “c in tutorialsbook” etc.

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