Pattern matching in switch in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pattern matching with type check

What is the output of this C# code using pattern matching in a switch expression?

C Sharp (C#)

object obj = 42;
string result = obj switch
{
    int i when i > 40 => "Greater than 40",
    int i => "Integer",
    string s => "String",
    _ => "Other"
};
System.Console.WriteLine(result);

A String

B Integer

C Other

D Greater than 40

💡 Hint

Look at the order of patterns and the value of obj.

The object is an int with value 42, which matches the first pattern 'int i when i > 40', so the output is 'Greater than 40'.

❓ Predict Output

intermediate

Pattern matching with property check in switch

What will this C# code print when using pattern matching on a record type?

C Sharp (C#)

record Person(string Name, int Age);

Person p = new("Alice", 30);
string category = p switch
{
    { Age: < 18 } => "Minor",
    { Age: >= 18 and < 65 } => "Adult",
    { Age: >= 65 } => "Senior",
    _ => "Unknown"
};
System.Console.WriteLine(category);

A Minor

B Adult

C Senior

D Unknown

💡 Hint

Check the Age property value and which pattern it matches.

The Person has Age 30, which fits the pattern 'Age: >= 18 and < 65', so the output is 'Adult'.

🔧 Debug

advanced

Identify the error in pattern matching switch

What error does this C# code produce when compiled?

C Sharp (C#)

object value = "hello";
switch (value)
{
    case int i:
        System.Console.WriteLine("Integer");
        break;
    case string s when s.Length > 5:
        System.Console.WriteLine("Long string");
        break;
    case string s:
        System.Console.WriteLine("String");
        break;
    case null:
        System.Console.WriteLine("Null");
        break;
}

A No error, code compiles and runs

B CS0161: Not all code paths return a value

C CS0152: The switch cases are unreachable due to order

D CS8120: A pattern is unreachable because a previous pattern matches all strings

💡 Hint

Look at the order of string cases and their conditions.

No compiler error. The guarded string case handles strings with Length > 5, and the general string case handles other strings. Both patterns are reachable.

📝 Syntax

advanced

Which switch pattern syntax is invalid?

Which of these C# switch case patterns will cause a syntax error?

A case int i when i % 2 == 0:

B case { Length: > 5 } s:

C case string s if s.StartsWith("A"):

D case null:

💡 Hint

Check the correct keyword for pattern guards in switch cases.

The keyword 'if' is invalid in switch case patterns; 'when' must be used for guards. Option C uses 'if' causing a syntax error.

🚀 Application

expert

Determine the final value after complex pattern matching

Given the following C# code, what is the value of 'result' after execution?

C Sharp (C#)

object data = new List<int> { 1, 2, 3 };
string result = data switch
{
    List<int> list when list.Count == 0 => "Empty list",
    List<int> list when list.Count > 0 && list[0] == 1 => "Starts with one",
    List<int> list => "Other list",
    _ => "Unknown"
};

A "Starts with one"

B "Empty list"

C "Other list"

D "Unknown"

💡 Hint

Check the list contents and which pattern matches first.

The list has elements and starts with 1, so it matches the second pattern and result is "Starts with one".