C# Variables & Keywords

In C#, a variable is a named storage location in memory that holds a value of a specific data type. Variables allow programs to store, modify, and retrieve data dynamically.

Declaring Variables

To declare a variable, specify the data type followed by the variable name:

int age;         // Declares an integer variable
string name;     // Declares a string variable
bool isActive;   // Declares a boolean variable
    

Initializing Variables

Variables can be assigned a value at the time of declaration or later:

int age = 25;             // Initialization during declaration
string name = "LoopCode";    // Initialization
bool isActive = true;     
    

Types of Variables

In C#, variables can be categorized based on their scope and lifetime:

• Local Variables: Declared inside a method or block. Accessible only within that block.

  
  void Demo() {
      int localVar = 10;   // local variable
      Console.WriteLine(localVar);
  }
              

• Instance Variables: Declared inside a class but outside methods. Each object has its own copy.

  
  class Person {
      public string name;  // instance variable
  }
  Person p = new Person();
  p.name = "Rahul";
              

• Static Variables: Declared with the static keyword. Shared among all objects of the class.

  
  class Counter {
      public static int count = 0;  // static variable
  }
  Counter.count++;
              

• Read-Only Variables: Declared with readonly. Value assigned once and cannot be changed.

  
  readonly int maxValue = 100;
              

• Constants: Declared with const. Value cannot be changed after declaration.

  
  const double PI = 3.14159;
              

Rules for Variable Names

• Must start with a letter or underscore (_)
• Cannot start with a number
• Cannot contain spaces or special characters (except _)
• Cannot be a C# reserved keyword
• Case-sensitive (age ≠ Age)

C# Keywords

Keywords are reserved words that have a special meaning in C#. They cannot be used as variable names.

• int, float, double
• if, else, for
• while, do, switch
• class, interface, namespace
• true, false, null

Example: Variables & Keywords

// Valid variable names
int age = 25;
string firstName = "Rahul";
bool isActive = true;

// Using var keyword
var number = 100;      // Compiler infers type int
var text = "Hello";    // Compiler infers type string

Console.WriteLine(age);
Console.WriteLine(firstName);
Console.WriteLine(isActive);
Console.WriteLine(number);
Console.WriteLine(text);
    

Best Practices

• Use meaningful variable names
• Use camelCase for variable names
• Do not use keywords as variable names
• Initialize variables when possible

Conclusion

Variables and keywords form the foundation of C# programming. Understanding how to declare, initialize, and use them correctly is essential for writing readable and maintainable code.

C# Variables & Keywords Quiz