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
Declaring (Creating) Variables
To create a variable, you must specify the type and assign it a value:
Where type is one of C++ types (such as
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:
Create a variable called myNum of type
int and assign it the value 15:
cout << myNum;
You can also declare a variable without assigning the value, and assign the value later:
myNum = 15;
cout << myNum;
Note that if you assign a new value to an existing variable, it will overwrite the previous value:
myNum = 10; // Now myNum is 10
cout << myNum; // Outputs 10
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):
myNum = 10; // error: assignment of read-only variable 'myNum'
A demonstration of other data types:
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.
cout object is used together with the
operator to display variables.
To combine both text and a variable, separate them with the
cout << "I am " << myAge << " years old.";
Add Variables Together
To add a variable to another variable, you can use the
int y = 6;
int sum = x + y;
cout << sum;
Declare Many Variables
To declare more than one variable of the same type, you can use a comma-separated list:
cout << x + y + z;
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).
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