C# Keywords & Identifiers

1. Keywords

• Reserved words in C# that have special meaning to the compiler.
• Cannot be used as variable names (unless escaped with @).
• Examples:
  • Access Modifiers → public, private, protected, internal
  • Control Flow → if, else, switch, case, for, while, break, continue, return
  • Exception Handling → try, catch, finally, throw
  • Data Types → int, string, bool, decimal, var
  • Modifiers → static, readonly, const, sealed, abstract, virtual

2. Contextual Keywords

• Words that are not reserved everywhere, but act as keywords in certain contexts.
• Examples:
  • async – used when defining an asynchronous method.
  • await – used only inside an async method to await a task.
  • partial – used to split a class across multiple files.
  • where – in LINQ or generic type constraints.

(These can sometimes be used as variable names outside those contexts — but not recommended.)

3. Identifiers

• Names you create for variables, methods, classes, interfaces, etc.
• Examples:
  • Customer, productService, GetOrders(), dbContext.
• Rules:
  • Must start with a letter or _.
  • Cannot contain spaces or special characters (besides _).
  • Cannot be a keyword (unless prefixed with @).
  • C# is case-sensitive (Product ≠ product).

4. Reserved Identifiers

• Words that the compiler keeps for future use or special meanings.
• Example: add, remove, yield.