C++ Variables
C++ 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 -123double- stores floating point numbers, with decimals, such as 19.99 or -19.99char- stores single characters, such as 'a' or 'B'. Char values are surrounded by single quotesstring- stores text, such as "Hello World". String values are surrounded by double quotesbool- stores values with two states: true or false
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;
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You can also declare a variable without assigning the value, and assign the value later:
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
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Constants
However, you can add the const keyword if
you don't want others (or yourself) to override existing values (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'
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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.
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:
Add Variables Together
To add a variable to another variable, you can use the +
operator:
Declare Many Variables
To declare more than one variable of the same type, you can use a comma-separated list:
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.
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 (
myVarandmyvarare different variables) - Names cannot contain whitespaces or special characters like !, #, %, etc.
- Reserved words (like C++ keywords, such as
int) cannot be used as names
