C++ អថេរ-Variables

 Variables are containers for storing data values.

In C++, there are different types of variables (defined with different keywords), for example:

• int - stores integers (whole numbers), without decimals, such as 123 or -123
• double - stores floating point numbers, with decimals, such as 19.99 or -19.99
• char - stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotes
• string - stores text, such as "Hello World". String values are surrounded by double quotes
• bool - stores values with two states: true or false

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Declaring (Creating) Variables

To create a variable, you must specify the type and assign it a value:

Syntax

type variable = value;

Where type is one of C++ types (such as int), and variable is the name of the variable (such as x or myName). The equal sign is used to assign values to the variable.

To create a variable that should store a number, look at the following example:

Example

Create a variable called myNum of type int and assign it the value 15:

int myNum = 15;
cout << myNum;

You can also declare a variable without assigning the value, and assign the value later:

Example

int myNum;
myNum = 15;
cout << myNum;

Note that if you assign a new value to an existing variable, it will overwrite the previous value:

Example

int myNum = 15;  // myNum is 15
myNum = 10;  // Now myNum is 10
cout << myNum;  // Outputs 10

Other Types

A demonstration of other data types:

Example

int myNum = 5;               // Integer (whole number without decimals)
double myFloatNum = 5.99;    // Floating point number (with decimals)
char myLetter = 'D';         // Character
string myText = "Hello";     // String (text)
bool myBoolean = true;       // Boolean (true or false)

You will learn more about the individual types in the Data Types chapter.

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Display Variables

The cout object is used together with the << operator to display variables.

To combine both text and a variable, separate them with the << operator:

Example

int myAge = 35;
cout << "I am " << myAge << " years old.";

Add Variables Together

To add a variable to another variable, you can use the + operator:

Example

int x = 5;
int y = 6;
int sum = x + y;
cout << sum;

Declare Many Variables

To declare more than one variable of the same type, use a comma-separated list:

Example

int x = 5, y = 6, z = 50;
cout << x + y + z;

C++ Identifiers

All C++ variables must be identified with unique names.

These unique names are called identifiers.

Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).

Note: It is recommended to use descriptive names in order to create understandable and maintainable code:

Example

// Good
int minutesPerHour = 60;

// OK, but not so easy to understand what m actually is
int m = 60;

The general rules for constructing names for variables (unique identifiers) are:

• Names can contain letters, digits and underscores
• Names must begin with a letter or an underscore (_)
• Names are case sensitive (myVar and myvar are different variables)
• Names cannot contain whitespaces or special characters like !, #, %, etc.
• Reserved words (like C++ keywords, such as int) cannot be used as names

Constants

When you do not want others (or yourself) to override existing variable values, use the const keyword (this will declare the variable as "constant", which means unchangeable and read-only):

Example

const int myNum = 15;  // myNum will always be 15
myNum = 10;  // error: assignment of read-only variable 'myNum'

You should always declare the variable as constant when you have values that are unlikely to change:

Example

const int minutesPerHour = 60;
const float PI = 3.14;