Mastering the use of variables in C++ from definition to practice

Updated: March 26, 2024 09:55:03 Author: Xiao Wan Ge,

Variables are containers used to store data values, in C++, there are different types of variables (using different keyword definitions), this article gives you an introduction to the use of variables in C++ from definition to practice records, interested friends follow the small series to see it

catalogue

C++ variable

C++ identifier

C++ constant

A note on constants

finally

C++ variable

A variable is a container used to store data values.

In C++, there are different types of variables (defined using different keywords), such as:

int- Store integers (no decimal points), for example123 或 - 123.
double- Store floating-point numbers with decimal points, for example19.99 或 19.99
char- Stores a single character, for example'a' 或 'B'. Character values are enclosed in single quotation marks
string- Store text, for example"Hello World". String values are enclosed in double quotes
bool- Stores values with two states:true 或 false

Declare (create) variables

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

grammar

type variableName = value;

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

To create a variable that should store numbers, refer to the following example:

Give an example

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

int myNum = 15;
cout << myNum;

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

Give an example

int myNum;
myNum = 15;
cout << myNum;

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

Give an example

int myNum = 15; // myNum is 15. myNum = 10; // myNum is now 10 cout << myNum; // Output 10

Other types

Demonstrations of other data types:

Give an example

int myNum = 5; // Integer (no decimal) double myFloatNum = 5.99; // floating-point number (with decimal points) char myLetter = 'D'; // string myText = "Hello"; // String (text) bool myBoolean = true; // Boolean value (true or false)

Display variable

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

To combine text and variables, use the << operator to separate them:

Give an example

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

Add variables

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

Give an example

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

C++ identifier

All C++ variables must be identified by a unique name.

These unique names are called identifiers.

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

Note: Descriptive names are recommended to create understandable and maintainable code:

Give an example

// OK int minutesPerHour = 60; // Yes, but it's not easy to understand what m is. int m = 60;

The general rule for naming variables is:

The name can contain letters, numbers, and underscores
Name must start with a letter or underscore (_)
Name is case sensitive (myVar and myvar are different variables)
The name cannot contain Spaces or special characters, such as! , #, %, etc.
Reserved words (such as C++ keywords, such as int) cannot be used as names

C++ constant

When you don't want someone else (or yourself) to change the value of an existing variable, use the const keyword (this will declare the variable as a "constant", i.e. unchangeable and read-only) :

Give an example

const int myNum = 15; // myNum will always be 15 myNum = 10; // Error: Attempt to assign read-only variable 'myNum'

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

Give an example

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

A note on constants

When you declare a constant variable, you must assign a value to it:

Give an example

Like this: const int minutesPerHour = 60;

However, this will not work

const int minutesPerHour; minutesPerHour = 60; // Error

finally

This article about learning to use variables in C++ : from definition to practice is introduced to this article, more related to the use of variables in C++ please search the previous articles of the script home or continue to browse the following related articles hope that you will support the script home in the future!

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