constant and their types in C++

In a way, the constant is used for constant values. When we declare a variable in constant variables, So these variables values never ever change during execution or running of a program i.e. their value remains fixed. When you declare the constant variable, we have to initialize it at the same time.

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some important facts about constant.

Constant can be any type of data type.

  • It has to be initialized at the time of the declaration of the Constant.
  • Once the value is assigned to the constants it is fixed. This cannot be changed later.
  • We can use constants in two ways, first by using the “const” keyword and second by using “#define” pre-processor.
  • They are also called literals.

defining constant in C++

  • To declare a variable as constant, we need to add the “const” keyword before the variable.
const data-type variable-name = value;
  • we can also use #define Pre-processor to define a constant,
#define data-type variable-name value;

Let’s consider with an example here,

using “const” keyword

#include <iostream>
using namespace std;

 int main()
  {
     const int FIRST = 10;
     const char NEXTLINE = '\n';
      const float SECOND = 0.1; 
     cout<<x<<y;
     cout<<z;
  return 0;  
 }

OUTPUT

5
0.1

using #define Pre-processor

#include <iostream>
using namespace std;

 int main()
  {
     #define FIRST 10;
     #define char NEXTLINE  '\n';
     #define float SECOND  0.1; 
     cout<<x<<y;
     cout<<z;
  return 0;
 }

OUTPUT

5
0.1

it is not good programming to use #define pre-processor to define a constant in C++.

Let’s more about constant,

constant type in C++

  •  numeric constant
  • characters constant

But they also have many types. You can understand this from the diagram given below-

constant in C++

 

numeric constant

It contains all kinds of numeric values, there are 2 types of numeric constant-

  • integer constant
  • floating constant

an integer constant is 3 types

  • decimal constant
  • Octal constant
  • Hexa-Decimal constant

decimal constant

it contains all the normal numeric values (both positive and negative). Whose base is 10 (0-9). like

octal constant–

It has base 8 (0-8). like-

const int x = 012; const int y=0200; const int z = 011;

hexadecimal constant –

it has Base 16 (0-9 and A-F).

const int x = 0x11; or const int y=0x2f1;

floating constant

It contains all the floating numeric type value. like-

const int x = 0.5;const int y= 0.10; const int 4.53;

Characters Constant

There are character values in it. Such as a name or “a” alphabet. It is divided into two parts-

  • character constant
  • string constant
Character Constant

There is a single character in it. In character constant, single quotes are used in the character, such as a character or alphabet

const char x = '5';
const char y = 'x';
const char z = ' '; // null
String Constant

There is a character of sequence or sentence. like someone’s name string constant is declared in double-quotes like-

const char name[ ] = "LearnC++";
const char y = ""; // null string
const char x[] = " " //  space
const char z[20]= 'learn C++ ';

we can declare a constant variable both locally and globally.


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