C# is a powerful and versatile language, and understanding its basic syntax is the first step towards mastering it. This lesson will cover the fundamental building blocks of C# code: variables, data types, and operators. These concepts are essential for writing any C# program, from simple console applications to complex web applications. By the end of this lesson, you'll have a solid foundation for building more advanced C# applications.

Variables in C#

Variables are named storage locations in a computer's memory that hold data. Think of them as labeled boxes where you can store different types of information. In C#, you must declare a variable before you can use it. This declaration involves specifying the variable's data type and its name.

Declaring Variables

The syntax for declaring a variable in C# is:

data_type variable_name;

For example:

int age; // Declares an integer variable named 'age'
string name; // Declares a string variable named 'name'
double salary; // Declares a double-precision floating-point variable named 'salary'

• int, string, and double are examples of data types, which we'll discuss in detail later.
• age, name, and salary are the names you choose for your variables. Variable names should be descriptive and follow certain rules:
  • They must start with a letter or an underscore (_).
  • They can contain letters, numbers, and underscores.
  • They are case-sensitive (age and Age are different variables).
  • They cannot be C# keywords (like int, string, class, etc.).

Initializing Variables

After declaring a variable, you can assign it a value. This is called initialization. You can initialize a variable at the time of declaration or later in your code.

int age = 30; // Declares an integer variable 'age' and initializes it to 30
string name = "John Doe"; // Declares a string variable 'name' and initializes it to "John Doe"

double salary; // Declares a double variable 'salary'
salary = 50000.00; // Initializes 'salary' to 50000.00

It's good practice to initialize variables when you declare them to avoid unexpected behavior. If you don't initialize a variable, C# assigns it a default value (e.g., 0 for numeric types, null for reference types like string).

Variable Scope

The scope of a variable determines where in your code you can access it. Variables declared inside a block of code (e.g., within curly braces {}) are only accessible within that block. This is known as block scope.

void MyMethod()
{
    int x = 10; // 'x' is accessible within MyMethod

    if (true)
    {
        int y = 20; // 'y' is accessible only within this 'if' block
        Console.WriteLine(x); // Valid: 'x' is accessible here
    }

    // Console.WriteLine(y); // Invalid: 'y' is not accessible here (out of scope)
    Console.WriteLine(x); // Valid: 'x' is accessible here
}

Variables declared outside any block (e.g., at the class level) have class scope and are accessible throughout the class. We'll explore class-level variables in more detail when we discuss classes in Module 2.

Data Types in C#

A data type specifies the kind of values a variable can hold. C# is a strongly-typed language, which means that every variable must have a declared data type, and the compiler enforces type safety. C# provides a rich set of built-in data types, which can be broadly categorized into: