Difference Between Constants and Variables in C

Last Updated : 12 Jul, 2025

The constants and variables in C are both used to store data. So it is essential to know the difference between the variables and constants in C so that we can decide which one to use based on the situation.

In this article, we will discuss the basic difference between a constant and a variable in C language.

Variables in C

A variable in simple terms is a storage place that has some memory allocated to it. It is used to store some form of data and retrieve it when required. Different types of variables require different amounts of memory and have some specific set of operations that can be applied to them.

C Variable Declaration

type variable_name;
type variable1_name, variable2_name, variable3_name;

A variable name can consist of alphabets (both upper and lower case), numbers, and the underscore '_' character. However, the name must not start with a number.

Example of C Variable

#include <stdio.h>
int main()
{
    // declaration and definition of variable 'a123'
    char a123 = 'a';

    // This is also both declaration
    // and definition as 'b' is allocated
    // memory and assigned some garbage value.
    float b;

    // multiple declarations and definitions
    int _c, _d45, e;

    // Let us print a variable
    printf("%c \n", a123);

    return 0;
}

Output:

Constants in C

The constants are those variables or values in the C which cannot be modified once they are defined in the program.

They have fixed values till the program's life.
We can only assign value to the constant in the declaration.
There can be any type of constant like integer, float, octal, hexadecimal, character constants, etc.

Example of C Constant

#include <stdio.h>

// Constants Macro
#define val 10

// Driver code
int main()
{
    // constant variables
    const float floatVal = 5.8;
    const char charVal = 'a';

    // printing constants
    printf("Integer Constant: %d\n", val);
    printf("Floating point Constant: %f\n", floatVal);
    printf("Character Constant: %c\n", charVal);

    return 0;
}

Output

Integer Constant: 10
Floating point Constant: 5.800000
Character Constant: a

Difference between Constant and Variables

The following table lists the differences between the constant and variables in C:

Constant	Variables
A constant is a variable or value that cannot be altered once defined.	A variable is a name associated with some memory location.
A constant is used to hold the fixed values which we can retrieve later but cannot change.	A variable is used to hold some value that can be changed according to the requirement.
The constants are generally stored in the text segment as they are read-only	The variables are stored inside a data segment, heap, or stack depending on the environment it is declared in.
We can only assign a value to the constant while defining it.	We can assign value to the variable anytime.
A constant can be defined by using #define or const keyword.	A variable can only be defined using the standard variable definition syntax.
Example: #define pi 3.14 const int pi = 3.14;	Example: int var = 25; var = 10;

Difference between Keyword and Identifier in C

sweetsubhashree2013

Improve

Article Tags :