Cpp - Introduction Constant Creation

Introduction

C++ has two types of constants: literal and symbolic.

The const keyword is used to create a "read only" variable.

It defines constant that cannot be modified and must be initialized during its definition.

const double pi = 3.1415947; 

The value of pi cannot be modified by the program.

A statement such as the following will result in an error message:

pi = pi + 2.0;               // invalid  

Demo

#include <iostream> 
using namespace std; 
int main() /*from   w ww.  j av a 2  s  .  c o m*/
{ 
   const double pi = 3.1415947; 
   cout << pi;
   return 0; 
}

Result

Symbolic constant

A symbolic constant is a constant represented by a name, just like a variable.

The const keyword precedes the type, name, and initialization.

Here's a statement that defines a constant:

const int Score = 5000; 

Defining Constants directive

The preprocessor directive #define can create a constant by specifying its name and value, separated by spaces:

#define Score 5000 

The constant does not have a type such as int or char.

The #define directive enables a simple text substitution that replaces every instance of Score in the code with 5000.

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