Constants in C

What are constants?

Constants in C are the fixed values that are used in a program, and its value remains the same during the entire execution of the program.

Example: 9,3.14,'T' etc.

Points to remember:

· 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 also called literals.

· It is considered best practice to define constants using only upper-case names.

How to define constants?
In C program we can define constants in two ways as shown below:

1. Using #define preprocessor directive
2. Using const keyword

1).Using #define preprocessor directive

This directive used to declare an alias name for existing variable or any value. We can use this to declare a constant as shown below:

Syntax:

#define IDENTIFIERNAME value

where IDENTIFIERNAME is the name given to constant and value is any value assigned to it.

Below is the C program to explain how to use #define to declare constants:

#include<stdio.h>

#define PI 3.14

int main(){

            int radius;

            float area;    

            //Ask user for radius of the cicle

            printf("\nEnter radius of circle:");

            scanf("%d",&radius);        

            //calculate areaof the circle

            area=PI*radius*radius;  

            printf("\nArea of the circle having radius %d is %f.\n",radius,area);      

            return 0;

}

Output:

2).Using const keyword 

Using const  keyword to define constants is as simple as defining variables, the difference is you will have to precede the definition with a const keyword.

Syntax:

const dataType IDENTIFIERNAME =value;

or

dataType const  IDENTIFIERNAME =value;

Example:

    const float rate=12.5;

Below program shows how to use const to declare constants of different data types:

#include<stdio.h> int main(){             const float PI=3.14;             int radius;             float area;             //Ask user for radius of the cicle             printf("\nEnter radius of circle:");             scanf("%d",&radius);                     //calculate areaof the circle             area=2*PI*radius;               printf("\nArea of the circle having radius %d is %f.\n",radius,area);                   return 0; }

Output:

Types of constants

1).Integer Constants

An integer is a numeric constant (associated with number) without any fractional or exponential part. There are three types of integer constants in C programming:

·                     decimal constant(base 10)

·                     octal constant(base 8)

·                     hexadecimal constant(base 16)

2. Floating-point constants

A floating point constant is a numeric constant that has either a fractional form or an exponent form.

3. Character constants

A character constant is created by enclosing a single character inside single quotation marks.Character constants have a specific set of integer values known as ASCII values (American Standard Code for Information Interchange).

Example: '9', 'T', ';'

 

4. String Literals

A string literal is a sequence of characters enclosed in double-quote marks. For example:

Example: "Techabaya", "2019".

Please comment if you find anything incorrect, or you want to improve the topic discussed above..