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Constants in C


In this post I'm gonna discuss what constants are actually in C. You can access my C programming full course in order to learn programming skills quickly.

When we talk about Constants in C, there are lots of questions arise,  which I will try to answer in this post.

So lets start discussing all the questions.

What are Constants in C?

C Constants are the most fundamental and essential part of the C programming language.

Constants in C are values or variables which can't be changed in the program, also called literals.

I mean contants are like variables, which value never changes during execution once defined.

For example: 40, 54, 'd', 2.4, "c programming tutorial" etc. are constants.

Types of Constant in C

C Constant can be classified as:

  • Integer constant
  • Real constant
  • Character constant
  • String constant

1. Integer Constant in C Language:

Integer Constants in C are refers to the sequence of digits. Range of integer constants is -32,768 to 32,767.

There are three types of integer constants in the C language:

Decimal constant (base 10)

     Decimal Digits: 0 1 2 3 4 5 6 7 8 9
     Example: 0. -8, 24 etc.

Octal constant (base 8)

    Octal Digits: 0 1 2 3 4 5 6 7
    Example: 421, 027, 233 etc.

Hexadecimal constant (base 16)

    Hexadecimal Digits: 0 1 2 3 4 5 6 7 8 9 A B C D E F
    Example: 0x3f, 0x5a, 0x541 etc.

2. Real Constant in C Language

Real constant in C refers to the numbers containing fractional parts like 45.25, are called real or floating points constant. The range of Real Constants is -3.4*1038 to 3.4*1038.

There are two form of writing Real constants:

Decimal Form: -2.0, 0.0000234

Exponential Form: -0.22E-5

3. Character Constant in C Language

Character Constant in C refers to the single character enclosed within a pair of single quote (' ') like 'A', 'd', '54', '8'. 

The range of Character Constants is -128 to 127.

4. String Constant in C Language

String constants in c refers to the sequence of characters enclosed in double quotes, and they may include letters, digits, special characters, and blank spaces.


“Hello”, “1987”, “?….!”, “x”, ” “, “” (null string constant)

Two ways to define constant in C

Now, we see,  How to use Constants in a C Program?

There are two ways to define constant in C programming

  • const keyword
  • #define preprocessor

1. C const keyword

In order to define constant in C programming, the const keyword is used.


 const type constant_name;

Lets understand declaration of constant using const keyword in C with example:


 int main(){   

    const float PI=3.14;   

    printf("The value of PI is: %f",PI);   

    return 0



 The value of PI is: 3.140000

Now, If we try to change the the value of PI constant, it will throw the compile time error. How? see:


 int main(){   

 const float PI=3.14;    


 printf("The value of PI is: %f",PI);   

    return 0



 Compile Time Error: Cannot modify a const object

2. C #define preprocessor

The another approach of defining constant in C is #define preprocessor.


 #define token value

Let's see an example of #define to define a constant in C:

 #include <stdio.h> 

 #define PI 3.14 

 main() { 





Conclusion of Constants in C

So we have learnt What are Constants in C, Types of Constants, and 2 ways to define constants in C.

I hope you have got clear about Constants in C.

If you have any doubt about C Constants then please ask me with comment.

Thanks for visit!

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