C++ Constants

Constants are like a variable, except that their value never changes during the program execution once defined.

What are Constants?

Constants refer to as fixed values, unlike variables whose value can be altered, constants - as the name implies does not change, they remain constant. Constant must have to be initialized at the time of creating it, and new values cannot be assigned later to it.

  • Constants are also called literals.
  • Constants can be any of the data types.
  • It is considered best practice to define constants using only upper-case names.

Constant Definition in C++

There are two other different ways to define constants in C++. These are:

  • By using const keyword
  • By using #define preprocessor

Constant Definition by Using const Keyword

Syntax:
const type constant_name;
Example:
#include <iostream>
using namespace std;

int main()
{
  const int SIDE = 50;
  int area;
  area = SIDE*SIDE;
  cout<<"The area of the square with side: " << SIDE <<" is: " << area << endl;
  system("PAUSE");
  return 0;
}
Program Output:

cplusplus-constants

It is also possible to put const either before or after the type.

int const SIDE = 50;

or

const int SIDE = 50;

Constant Definition by Using #define preprocessor

Syntax:
#define constant_name;
Example:
#include <iostream>
using namespace std;

#define VAL1 20   
#define VAL2  6
#define Newline '\n'

int main()
{
   int tot; 
   tot = VAL1 * VAL2;
   cout << tot;
   cout << Newline;
}