Variables in C++

Variables and their Types

 What is Variables?

         In programming, a variable is a value that can change, depending on conditions or on information passed to the program. Typically, a program consists of instruction s that tell the computer what to do and data that the program uses when it is running.

 For example: num=20;

How to Declare Variable in C++ SYNTAX? 

Single Variable Declaration

  datatype variable_name = value;

 
For example:

  int number= 10;

 Multi Variable Declaration

  datatype variable_name1 = value1  ,variable_name2=value2;

 
For example:

  int number1= 10 , number2 =12;

Types of Variable

Types	Length	Range
unsigned char	8 bits	0 to 255
char	8 bits	-128 to 127
unsigned int	32 bits	0 to 4,294,967,295
short int	16 bits	-32,768 to 32,767
int	32 bits	-2,147,283,648 to 2,147,283,647
unsigned long	32 bits	0 to 4,294,967,295
enum	16 bits	-2,147,283,648 to 2,147,283,647
long	32 bits	-2,147,283,648 to 2,147,283,647
float	32 bits	3.4 x 10^-38 to 3.4 x 10^ +38
double	64 bits	1.7 x 10^-308 to 1.7 x 10^ +308
long double	80 bits	3.4 x 10^4932 to 3.4 x 10^ +4932
far	32 bits

 

Types of variables based of their Scope:

Variable scope is a location in a program where the value of the variable is available. Every variable has its scope. According to scope there are two types of variables in C++ local and global.

Local variable is a variable declared within a function. The scope of local variables is the body of the function, in which the variable is declared. Local variable can be initialized by a constant or an expression corresponding to its type.
Global variable is a variable declared beyond all functions. The scope of global variables is the entire program. A global variable can be initialized only by a constant corresponding to its type (and not expression). Global variables are initialized only once before stating the execution of special functions.

 Example of Global variables:
 

#include<iostream>

using namepsace std;

int value= 10;

int main(){

int value2 =20;
cout<< value <<"\n"<< value2 <<endl;
return 0;
}

Output:

10 12

Example of local Variables

 

#include<iostream>
using namespace std;

int funct(){
 int val =10;
}
int main(){
cout << val<<endl;
return 0;
}

Output Compile time error, because we are trying to access the variable val outside of its scope. The scope of val is limited to the body of function Funcnt(), inside those braces.