Variables in C++

A variable provides us with named storage that our programs can manipulate. Each variable in C++ has a specific type, which determines the size and layout of the variable’s memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

Name of variable: It refers to an identifier that represents a memory location.

Address of variable: It refers to the memory location of the variable.

Contents of variable: It refers to the value stored in memory location referred by variable.

Variables in C++ Declaration

A variable must be defined before you can use it in a program. When you define a variable the type is specified and an appropriate amount of memory reserved. This memory space is addressed by reference to the name of the variable. A simple declaration has the following syntax:

SYNTAX: data_type variable_name;

Data_type: It indicates types of data that can be stored in a variable.

Variable_name: It refers to the memory location of a variable.

Example:

Different types of variables are declared as follows:

      int marks;
      float average;
      char grade; 
      double salary;

Rules for declaration Variables

Following are some rules for naming variable in C++ language:

• Variable may include letters, numbers, and underscores (_).
• The first character of the variable must be a letter or underscore _. The use of underscores is not recommended. The variable 9minute, #home, and 2kg are invalid.
• Blank spaces are not allowed in variable names. The variable my var and your car are invalid.
• Both upper and lower cases are allowed. A user-defined variable is conventionally written in lower case. The constants are conventionally written in upper case.
• Special symbols cannot be used as the variable names.
• Reserved words cannot be used as the variable names. the names int, void, and while are invalid variables.
• A variable can be up to 31 characters long for many compilers. If a variable consists of more than 31 characters, only the first 31 characters will be used. The remaining characters will be ignored.
• A variable can be declared only for one data type.

The variable must be meaningful and readable. It helps the user understand the purpose of the variable. For example, a variable to store the marks of the student should be capitalized Subjects. If a variable consists of multiple words, the first letter of each word should be capitalized to increases readability. A variable MyCarNo is more readable than mycarno.

Example:

Some example of valid variables:

Subject                        mar_1              _temp              first_name                               zoetropefilm

Variables in C++ initialization

A variable can be initialized, i.e. value can be assigned to the variable, during its definition. Initialization is achieved by placing the following immediately after the name of
the variable:

• an equals sign (=) and an initial value for the variable or
• round brackets containing the value of the variable.

SYNTAX:

type_name variable= value;

Example:

      int n= 100;
      int x=50, y = 30;
      char grade = `A`;  
      float average = 50.66;

C++ Program Introduction