C++ Variables

WHAT IS VARIABLES?

A variable provides named storage that manipulate the program. The name of a variable is called an identifier.  It should be related name. You can give a variable any name you want, as long as it is a valid identifier. Variables are used to store data. Every C++ variable has a:

Name -- variable name like price 

Type -- variable type like integer, string

Size -- determined by the type

Value -- the data stored in the variable's memory location

Address -- the starting location in memory where the value is stored

Syntax:

data_type variable_name;

data_type variable_name1, variable_name2, variable_name3;

Example:

/* variable definition */

int    marks;

char   ch;

float  unit;

double meter_to_cm;

Variables Declaration in C++

     C++ Declaration requires every variable to be declared with its type before its first use.

   int marks;

Variable Initialization in C++

     Variables can be initialized and initial value can be assigned along with their declaration.

   int marks=600;

    int price,tax;  //For declaration multiple variables;

RULES FOR NAMING VARIABLES

·         Variable name range in environment 1 to 31 character and in Visual C++ can range from 1 to 255 characters Variable names.

Example:

float productCost; //range 11

·         All variable names must start with an alphabet or an Underscore ( _ ). 

Example:

char _price;

float cost;

·         After the first initial letter, variable names can also contain numbers.

Example:

double a1, a3;

·         No spaces or special characters, however, are allowed.

Example:

float product price //wrong variable name with space

·         Uppercase characters are distinct from lowercase characters.

Example:

float PRICE;

float price;

·         You cannot use a C++ keyword (reserved word) as a variable name , for check C++ reserve keyword click here

Example:
float char; // char is keyword and not allowed variable name

SCOPE OF VARIABLE IN C++

A scope is a region of the program and broadly speaking there are two places, where variables can be declared.

Local Variable

Variables that are declared inside a function or block are local variables. They can be used only by statements that are inside that function or block of code.

Example of Local Variable

#include <iostream> //header file

using namespace std;

int main () {  //main

   float price; //Local variable declaration:

   cout << price; //output

   return 0;

}

Global Variable

Global variables are variables that are often declared outside the main() function. The variable scope is the full file where the variable is defined.

The global variable can be defined as below.

Example of Global Variable

#include <iostream> //header file

using namespace std;

float price; //Global variable declaration:

int main () {  //main

   cout << price; // output

   return 0;

}

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