JavaScript Error

Variables

Variables in C++ are containers used for storying data values of specific data types.

The following keywords are used to define different types of commonly used variables:

• int : integers (whole numbers), without decimals. For example: 1234 or -1234
• float : single-precision decimal number. For example: 98.6f
• double : double-precision decimal number number. For example: 3.14159 or -53.289334
• char : single characters, such as 'a' or 'B'. When assigning the Char value to the Char variable, its value should be surrounded by single quotes
• string : text containing zero or more characters. For example, "Hello World". When assigning the String value to the String variable, its value should be surrounded by double quotes
• bool : boolean value with two states: true or false

Declaring and Assigning Variables

To declare (i.e. create) a variable, the variable type must be specified when the variable name is defined. A value can be assigned to a variable either at the moment it was declared, or some time after it is declared:

// syntax format for declaring a variable and settings its value
type variableName = value;

// syntax format for declaring a variable without settings its value
type variableName;

With the Syntax formats shown above, substitute type with one of C++ variable type keywords (such as int), and variableName with the desired name of the variable itself (such as x or tempValue). The equal sign (=) is used to assign a value to the variable. Always close the instruction with the semicolon (;).

Best Practice: When naming your variables, it is best to stick to names that start with a letter, and steer clear of starting with double underscores (__) or underscored capitalized names (_CapitalizedName), since they often result in unexpected conflicts with reserved system variables.

Follow these rules when creating variable names:

• Each variable name should be unique within its scope. If you declare two variables with the same name in the same scope, the compiler will throw an error for redefinition.
• Variable names can contain letters, digits and underscores
• Variable names must begin with a letter or a single underscore (_)
• Variable names are case-sensitive : myVar and myvar are treated as two different variables
• Variable names cannot contain any whitespaces or special characters like ~,!,@,#,$,%,^,&,*,(,), etc.
• Variable names cannot be the same as compiler Reserved words. For example you cannot use int as a variable name because the system has reserved it to be used to define a variable data type of int.

The following is an example of how to create a variable that will be used to store a number:

// declare the variable and assign it a value
int myNum = 42;

// output the value contained within the variable
cout << myNum;

Or if you need or want to declare the variable first, and then assign it a value afterwards, you can do that as well:

// declare the variable
int myNum;

// assign it a value
myNum = 42;

// output the value contained within the variable
cout << myNum;

If you assign a new value to an existing variable, it will overwrite the previous value.

Note : Make certain that the new value is of the same variable type (i.e. int) as the variable is, otherwise bugs will be introduced and unexpected results may occur.

// declare the variable and assign it a value
int myNum = 42; // myNum = 42

// output the value contained within the variable
cout << myNum; // outputs 42

// assign the variable a new value
myNum = 1298; // myNum = 1298

// output the value contained within the variable
cout << myNum; // outputs 1298

Other Examples

The following is an example of how to declare variables of each of the different data types:

int myNum = 42;
float myFloat = 98.6;
double myDouble = 3.14159;
char myChar = 'A';
string myString = "Hello World";
bool byBool = false;

Display Value

To display the value of the variable, you can use the cout object together with the << operator. You can also combine both string text and a variable, separating them with the << operator, for example:

int myName = "Timmy";
int myAge = 53;
double myNetWorth = 1289.73;

cout << myName << " is " << myAge << " years old, and only has $" << myNetWorth << " in savings.";

Modifiers

Numerical data type variables can also have a modifier, to customize the base type:

• short, long, long long - used to vary the size of int
• signed, unsigned - allow negative or only positive values

unsigned int myScore = 100;
long long myBigNumber = 9000000000;

Derived Data Types

Data types can be derived and constructed from fundamental types:

• Arrays : float scores[5];
• Functions : double calculate(int x, int y);
• Pointers : int* myPointer = &myAge;
• References : int& myRef = myAge;

User-Defined Data Types

C++ also allows you to create and develop your own structures for more advanced designs:

• struct : Group related variables
• class : Object-oriented encapsulation
• union : Share memory among different variables
• enum : Named constants
• typedef / using : Create aliases for types

struct myStruct = { int x, y; };
enum myColors { RED, GREEN, BLUE };

Arithmetic Operations On Variables

To perform an arithmetic operation (i.e. add, subtract, multiply, divide, etc...) on and with variables, you can use the variable in place of the value:

int x = 3;
int y = 12;
int sum = x + y;

cout << sum;

Declare Multiple Variables

C++ allows you to declare more than one variable of the same data type, and assigning each their own value, by using a comma-separated list:

int x = 3, y = 74, z = 12;

cout << x + y + z;

You can also assign the same value to multiple variables of the same data type in one line:

int x, y, z;
x = y = z = 25;

cout << x + y + z;

Final Thoughts

Thank you for reading, I hope you found this blog post (tutorial) educational and helpful.

	(0)
	(0)