Variables

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Published May 6, 2021Updated Oct 18, 2024
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A variable refers to a storage location in the computer’s memory that one can set aside to save, retrieve, and manipulate data. Variables act as containers for storing information that can be changed or updated during the execution of a program.

Declare a Variable

To declare a variable, the type of data the variable will hold must be specified, followed by the variable name. Optionally, a value can be assigned to the variable at the time of declaration:

type name = value;

So to create a variable called score of type int and assign it the value 0:

int score = 0;

Display Variables

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

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

int myAge = 30;


std::cout << "I am " << myAge << " years old.";

The output would be:

I am 30 years old.

Data Types in Variables

Each variable in programming has a type, which defines the kind of data it can hold. Here are some common data types:

  • int: for integers (whole numbers), e.g.,
int score = 10;
  • float: A single-precision floating-point number, typically occupying 4 bytes (32 bits). It offers less precision and is used when memory efficiency is more important than accuracy, e.g.,
float pi = 3.14159;
  • double: A double-precision floating-point number, typically occupying 8 bytes (64 bits). It provides more precision and is the default choice when you need to store decimal numbers in C++.
double pi = 3.14159265358979323846;
  • char: A single character, e.g.,
char letter = 'A';
  • bool: for boolean values (true or false), e.g.,
bool isAdmin = true;

Example

The below example shows the usage of variables:

#include <iostream>


int main() {
  int age = 25;
  double temperature = 36.6;
  char initial = 'R';
  bool isSunny = true;


  std::cout << "Age: " << age << std::endl;
  std::cout << "Temperature: " << temperature << "°C" << std::endl;
  std::cout << "Initial: " << initial << std::endl;
  std::cout << "Is it sunny? " << (isSunny ? "Yes" : "No") << std::endl;


  return 0;
}

The code above generates the following output:

Age: 25
Temperature: 36.6°C
Initial: R
Is it sunny? Yes

Codebyte Example

Run the codebyte to understand how variables work:

Code
Output
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Variables
Constant Variables
Defines variables in C++ whose values cannot be altered after they are set.
Global Variables
Variables that are defined outside of all functions are called global variables.
Local Variables
A variable defined inside a function body between braces is called a local variable.
Mutable Variables
Mutable variables are variables that can be modified even within constant functions.
Volatile Variables
Ensures variables avoid compiler optimization, allowing correct access when their values may change due to external factors.
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