C#.NET — Validity of case labels in switch with variables. int i, j, id = 0; switch (id) { case i: Console.WriteLine("I am in Case i"); break; case j: Console.WriteLine("I am in Case j"); break; }

Introduction / Context:This question checks the requirement that C# switch case labels be compile-time constants, not variables whose values are only known at runtime.

Given Data / Assumptions:

• Switch discriminant: id (an int).
• Case labels: i and j, both variables.

Concept / Approach:In C#, case labels must be constant expressions (e.g., literals, const fields, or enum members). Using non-const variables as case labels is a compile-time error.

Step-by-Step Solution:

Verification / Alternative check:Replace i or j with const int K = 5; case K: ... and the code would compile. Similarly, enum members are allowed because they are constants.

Why Other Options Are Wrong:

• No default case is not itself an error.
• Printing "I am in Case i" or "Case j" cannot occur because compilation fails.
• "There is no error" contradicts the language rule.

Common Pitfalls:Confusing switch-case rules from other languages or assuming any expression is permitted in labels. C# enforces constants for determinism at compile time.

Final Answer:The compiler will report case i and case j as errors since variables cannot be used in cases.