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Variables & Constants in C are formed by combining alphabets, numbers, and special symbols. Let us see what are ‘constants’ and ‘variables’ in C.

Variables:

• An entity that may change during program execution is known as a variable.
• Variables are the names assigned to the memory locations.
• These locations can contain integer, real, or character constants.
• The rules for creating variables are the same as that of identifiers.
• Variable declaration is a must at the start of the program.

The syntax for declaring a variable:

dataType variable_name;

Example:

int age;
float sum;

Here, age and sum are variables whereas, int and float are data types in C.

Constant:

• A constant is an entity that doesn’t change during program execution.
• Constant is also called literal.
• There are different types of constants in C programming.

Constants	Examples
Integer constants	426,+78,-2900
Real or Floating-point constants	+34.09,-98.345,88.456
Character constant	‘a’, ‘5’, ‘=’, ‘*’
Octal Constant	021, 033, 046
String Constant	“c”, “c program”, “c in javatpoint”
Hexadecimal Constant	0x2a, 0x7b, 0xaa

There are two ways to define constant in C programming.

1. const keyword
2. #define preprocessor

const keyword:

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

output:

The value of PI is: 3.14

here,

const float PI=3.14

as a result, the value of variable PI is set to 3.14 which cannot be changed during program execution.

#define preprocessor: The #define preprocessor is used to define constant. We will know more about the #define preprocessor directive later on.

#include<stdio.h>
#define PI 3.14
int main(){    
float area=PI*5*5;   
printf("The Area of circle is: %f",area);    
    return 0;  
}     

output:

The Area of circle is: 78.5

note: also read about Identifiers in C & Keywords in C.

next: Data Types in C

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