Constants In C

A constant is a value or variable that can't be changed in the program, for example: 10, 20, 'a', 3.4, "c programming" etc.

There are different types of constants in C programming.

List of Constants in C

Methods of defining constant in C

There are two methods to define constant in C Programming Language.

1) const keyword

The const keyword is used to define constant in C programming.

const float PI=3.14;  

Now, the value of PI variable can't be changed.

#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: 3.140000

If you try to change the the value of PI, it will render compile time error.

#include<stdio.h>    

int main(){    

       const float PI=3.14;     

       PI=4.5;    

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

      return 0;  

  }     

Output:

Compile Time Error: Cannot modify a const object

2) #define preprocessor

The #define preprocessor is also used to define constant. The details of #define preprocessor directive has been discussed further in the tutorials.