C++ Constants

In C++ Language Constants is a fixed values that do not change during the execution of a program. These are also called Literals.

‘Pi’ is the best example for constants. Pi value is 3.414. which is fixed.

Syntax:

const data_type variable_name;

The type of constants that are listed below:

• Numeric Constants
• Character Constants

Numeric Constants:

In numeric constants, there are two types of other constants namely “Integer Constants and Real Constants”. The brief details about the two type of constants are given below.

1.Integer Constants:

Integer constants refer to a sequence of digits. There are three types of integers namely ‘decimals, octal and hexadecimal’.

• Decimal Integers consist of a set of digits i.e., 0 to 9, preceded by an optional – to the + sign.
• An Octal Integer constants consist of the combination of the digits from the set 0 through 7, with a leading 0.
• A hexadecimal integer consists of a sequence of digits preceded by 0X and 0x.

2.Real Constants:

Integer numbers are inadequate to represent the quantities that vary continuously. Such as prices, temperatures, distances, heights, and so on. Such type of numbers is called real numbers. There are decimal notation, exponential notation in Real Constants.

Character Constants:

In Character Constants there are two more constants are available namely “Single Character constants and String Constants.”

1.Single Character Constants

It defines a single character enclosed within a pair of single quote marks.

Ex: ‘4’, ‘Q’

2.String Constants

A sequence of character enclosed in " " quotes is called String Constant. The character may be in letters, numbers, special characters and blank spaces.

Ex: “Hello”, ”1976”’.

Defining C++ Constants

There are two different ways in C++ to define constants

• const keywords
• #define preprocessor

const keywords

In C++ programming the const keyword is used to define constants with a specific type.

Syntax

const data type variable = value;

Example

#include <iostream>  
using namespace std;

int main(){    
	int r=10;
    float area;
    const float PI=3.14;  
    area=PI*r*r;  
    cout << "The value of PI is " << area << endl;    
    return 0;  
} 

The #define Preprocessor

To use #define preprocessor to define a constant in C++ programming.

Syntax

#define identifier value 

Example

#include <iostream>  
#define Radius 20  
using namespace std;   


int main(){    
	float area;
    const float PI=3.14;  
    area=PI*Radius*Radius;  
    cout <<"The value of PI is "<< area << endl;     
    return 0;  
}