Switch expressions with patterns in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of switch expression with type patterns

What is the output of the following C# code using switch expressions with type patterns?

C Sharp (C#)

object value = 42;
string result = value switch
{
    int i => $"Integer: {i}",
    string s => $"String: {s}",
    _ => "Unknown"
};
System.Console.WriteLine(result);

A String: 42

B Integer: 42

C Unknown

D Compilation error

💡 Hint

Check the type of the variable 'value' and how the switch expression matches patterns.

The variable 'value' is an int with value 42. The switch expression matches the 'int i' pattern and returns "Integer: 42".

❓ Predict Output

intermediate

Switch expression with property pattern output

What will be printed by this C# code using a switch expression with a property pattern?

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 Unknown

B Minor

C Senior

D Adult

💡 Hint

Look at the Age property of the Person record and which pattern it matches.

The Person has Age 30, which matches the pattern { Age: >= 18 and < 65 }, so the result is "Adult".

🔧 Debug

advanced

Identify the error in this switch expression with tuple patterns

This C# code uses a switch expression with tuple patterns. Which option correctly describes the error it produces?

C Sharp (C#)

var point = (x: 3, y: 4);
string quadrant = point switch
{
    ( > 0, > 0 ) => "First",
    ( < 0, > 0 ) => "Second",
    ( < 0, < 0 ) => "Third",
    ( > 0, < 0 ) => "Fourth",
    _ => "Origin or axis"
};
System.Console.WriteLine(quadrant);

A Compilation error due to missing parentheses around relational patterns

B Runtime NullReferenceException

C Output: First

D Output: Origin or axis

💡 Hint

Check if the tuple patterns and relational patterns syntax are correct and what the values are.

The tuple (3,4) matches the pattern ( > 0, > 0 ) so the output is "First". The syntax is valid in C# 9+.

📝 Syntax

advanced

Which switch expression syntax is correct for matching a string prefix?

Which option shows the correct C# switch expression syntax to match a string starting with "Hello" using a pattern?

A string greeting = input switch { string s when s.StartsWith("Hello") => "Hi", _ => "Bye" };

B string greeting = input switch { string s if s.StartsWith("Hello") => "Hi", _ => "Bye" };

C string greeting = input switch { string s => s.StartsWith("Hello") ? "Hi" : "Bye" };

D string greeting = input switch { string s where s.StartsWith("Hello") => "Hi", _ => "Bye" };

💡 Hint

Recall the correct keyword for adding a condition in a switch expression pattern is 'when'.

Option A uses 'when' correctly to add a condition in the pattern. Options B and D use invalid keywords 'if' and 'where'. Option A is a valid expression but not a pattern with condition.

🚀 Application

expert

Determine the number of items in the dictionary created by this switch expression

Consider this C# code that uses a switch expression inside a dictionary initializer. How many key-value pairs will the resulting dictionary contain?

C Sharp (C#)

var inputs = new object[] { 1, "two", 3.0, null };
var dict = new Dictionary<object, string>();
foreach (var item in inputs)
{
    dict[item] = item switch
    {
        int i => $"Int {i}",
        string s => $"Str {s}",
        null => "Null",
        _ => "Other"
    };
}
System.Console.WriteLine(dict.Count);

A 4

B 3

C 2

D 1

💡 Hint

Check how many unique keys are added to the dictionary and if any keys are overwritten.

The dictionary keys are the original objects: 1 (int), "two" (string), 3.0 (double), and null. All are unique keys, so the count is 4.