C Constants

In this lesson, you will learn about Constants in C, and their usages, along with examples to better understand the topic.

C Constants

As the name indicates, a constant is an identifier that, once defined, cannot modify through the program’s execution. Constant has some properties like it is case-sensitive, always uppercase, and cannot be undefined. By convention, the constant’s name begins with a letter or underscore, followed by any numbers, underscores, or letters. Constants have, by default, global scope throughout the whole program.

Basic Syntax

const double PI = 3.14;

Example of Constants in C

// Example of constant statement
#include <stdio.h>
int main ()
{
  const int var = 2050;
  printf ("Constant value %d\n", var);
  return 0;
}

Output

Constant value 2050

Can you reassign a value to a constant?

Once a constant is declared and assigned a value, it cannot be changed. In the example below, the program will throw an error as, later in the program, you try to change its value.

// Example of constant statement
#include <stdio.h>
int main ()
{
  const int var = 2050;
  var = 2060;
  printf ("Constant value %d\n", var);
  return 0;
}

Output

error: assignment of read-only variable ‘var’

In the next lesson, you will learn about the different Data Types available in the C Programming Language.