Constant in C language

Amit Kumar  Print 
25 Oct 2012
09 Aug 2018
Intermediate
18.8K

Constants

This tutorial will cover Constants in C. Constants refers to the fixed values that do not change during the execution of a program. A "constant" is a number, character, or character string that can be used as a value in a program. Use constants to represent floating-point, integer, enumeration, or character values that cannot be modified. C supports several types of constants that I am discussing in this article.

There may be a situation in programming that the value of certain variables to remain constant during execution of a program. In doing so we can use a qualifier const at the time of initialization.
For example :

const float pie =3.147;
const int radius =4;
const char c = 'A';
const char name[] = "Samina Kauser";

In C constant can also be used using preprocessor directive
For example :

 #define FIRST_NUMBER 1

Note

  1. const is a new data type qualifier in C defined by ANSI

Types of constant in C Language

  1. Primary Constant

    Primary Constant have following sub categories

    • Integer Constant

    • Real constant

    • Character constant

  2. Secondary Constant

    Secondary Constant have following sub categories

    • Array

    • Pointer Structure

    • Union

    • Enum

Using Constant In Our Program

(a) Constant definitions typically follow the #include directives at the top of C source code:

#include<stdio.h>
#define SPEEDLIMIT 55
#define RATE 15
#define FIRST_TICKET 85
#define SECOND_TICKET 95
#define THIRD_TICKET 100
int main()
 { 
 int total,fine,speeding; puts("Speeding Tickets\n"); 
/* first ticket */ 
speeding = FIRST_TICKET - SPEEDLIMIT; 
 fine = speeding * RATE; 
 total = total + fine;
 printf("For going %d in a %d zone: $%d\n",FIRST_TICKET,SPEEDLIMIT,fine); 
/* second ticket */ 
 speeding = SECOND_TICKET - SPEEDLIMIT; 
 fine = speeding * RATE; 
 total = total + fine;
 printf("For going %d in a %d zone: $%d\n",SECOND_TICKET,SPEEDLIMIT,fine); 
/* third ticket */ 
speeding = THIRD_TICKET - SPEEDLIMIT; 
 fine = speeding * RATE; 
 total = total + fine;
 printf("For going %d in a %d zone: $%d\n",THIRD_TICKET,SPEEDLIMIT,fine); 
/* Display total */
 printf("\nTotal in fines: $%d\n",total);
 return(0);
 } 

(b) Constant using const keyword C programming:

When declaring a const variable, it is possible to put const either before or after the type: that is, both

 int const a = 15; 

Or

 const int x = 15; 

Following is a simple example

 main() 
{
 const float pi = 3.14;
 float area_of_circle;
 area_of_circle = pi*r*r;
 printf("Area of circle is :%f",area_of_circle);
 } 
What do you think?

In this article I try to explain the concept of constants it's usage and it's types in C language. I hope you will be beneficial by this article. Comment and critics are welcome.

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