A variable is a reserved space in memory with a symbolic name (identifier), in which we can store a value of a specific type.
Variables allow us to store temporary data that we can use later throughout our program.
If you want to learn more about Variables
check the Introduction to Programming Course read more
Variable Declaration
Declaring a variable in C# involves specifying its type and giving it a name. The basic syntax for declaring a variable is:
type variableName;For example, to declare an integer variable called age:
int age;Default Values
In C#, uninitialized variables are assigned default values (depending on their type).
Value Types
For value types, the default values are:
| Type | Default Value |
|---|---|
| int | 0 |
| float | 0.0f |
| double | 0.0d |
| char | '\0' (null Unicode character) |
| bool | false |
Reference Types
For reference types, the default value is always null, which indicates that the variable does not reference any location in memory.
string str; // str is null by default
int[] array; // array is null by default
object myObject; // object is null by default.This leads to one of the most common errors in programming. If you access a Reference Type variable before creating it, you will get a null exception error because your variable contains nothing.
Before using a Reference Type variable, you must assign it an instance, or you will have a runtime error (i.e., when the program is running)
Assigning Values
Assigning a value to a variable is giving it an initial value or modifying the value it contains. The syntax for assigning a value to a variable is:
variableName = value;For example, to assign the value 25 to the variable age:
age = 25;It is also possible to declare and assign a variable in a single line:
int age = 25;Practical Examples
Let’s look at some very simple examples of using variables in C#. These examples show how to declare and use variables to perform calculations and manage data.
Student Data Management
In this example, we show how to manage basic data of a student, such as their name and age. This example illustrates how to declare and assign values to variables of different data types.
// We declare variables
public string name; // for the student's name
public int age; // for the student's age
// We assign values to the variables
name = "Ana";
age = 21;
// We print the student's data to the console
Console.WriteLine($"{name} is {age} years old");Circle Area Calculation
In this example, we calculate the area of a circle using a basic mathematical formula. A constant is declared for the value of PI and a variable for the radius of the circle.
// We declare a constant for the value of PI
const double PI = 3.14159;
// We declare a variable for the radius of the circle
double radius = 5.0;
// We calculate the area of the circle using the formula: area = PI * radius^2
double area = PI * radius * radius;
// We print the result to the console
Console.WriteLine($"The area of the circle is: {area}");:::::::