Property patterns in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested property pattern matching

What is the output of this C# code using property patterns?

C Sharp (C#)

record Address(string City, string Country);
record Person(string Name, Address Address);

var person = new Person("Alice", new Address("Paris", "France"));

string result = person is { Address: { City: "Paris" } } ? "Match" : "No match";
Console.WriteLine(result);

A Compilation error

B No match

C Match

D Runtime exception

💡 Hint

Check how nested property patterns match inner properties.

The pattern checks if the Address property has a City equal to "Paris". Since it does, the result is "Match".

❓ Predict Output

intermediate

Output of property pattern with discard

What will this C# code print?

C Sharp (C#)

record Product(string Name, decimal Price);

var product = new Product("Book", 12.99m);

string output = product is { Price: > 10, Name: _ } ? "Expensive" : "Cheap";
Console.WriteLine(output);

A Compilation error

B Runtime exception

C Cheap

D Expensive

💡 Hint

The discard (_) means any Name is accepted.

The pattern checks if Price is greater than 10 and ignores Name. Since Price is 12.99, it prints "Expensive".

❓ Predict Output

advanced

Output of property pattern with nested null property

What is the output of this code?

C Sharp (C#)

record Engine(int Horsepower);
record Car(string Model, Engine? Engine);

var car = new Car("Sedan", null);

string result = car is { Engine: { Horsepower: > 200 } } ? "Powerful" : "Not powerful";
Console.WriteLine(result);

A Not powerful

B Powerful

C NullReferenceException

D Compilation error

💡 Hint

Property patterns safely handle null nested properties.

The pattern checks if Engine is not null and Horsepower > 200. Since Engine is null, it does not match and prints "Not powerful".

❓ Predict Output

advanced

Output of property pattern with multiple conditions

What will this code print?

C Sharp (C#)

record Employee(string Name, int Age, string Department);

var emp = new Employee("John", 30, "HR");

string output = emp is { Age: (>= 18 and <= 65), Department: "HR" } ? "Eligible" : "Not eligible";
Console.WriteLine(output);

A Runtime exception

B Eligible

C Compilation error

D Not eligible

💡 Hint

Check the combined conditions with 'and' in property patterns.

The pattern matches employees aged between 18 and 65 in the HR department. John meets both conditions, so output is "Eligible".

❓ Predict Output

expert

Output of property pattern with positional and property patterns combined

What is the output of this code?

C Sharp (C#)

record Point(int X, int Y)
{
    public string Quadrant => (X, Y) switch
    {
        (> 0, > 0) => "First",
        (< 0, > 0) => "Second",
        (< 0, < 0) => "Third",
        (> 0, < 0) => "Fourth",
        _ => "Origin or axis"
    };
}

var p = new Point(5, -3);

string result = p is { X: > 0, Y: < 0 } ? p.Quadrant : "Unknown";
Console.WriteLine(result);

A Fourth

B First

C Unknown

D Compilation error

💡 Hint

Combine property patterns with positional pattern logic inside the property.

The pattern matches X > 0 and Y < 0, which is the fourth quadrant. The Quadrant property returns "Fourth".

Practice

1. What is the main purpose of using property patterns in C#?

easy

A. To declare new properties in a class

B. To create new objects with default property values

C. To check multiple properties of an object in a clear and concise way

D. To override methods based on property values

Solution

1. Step 1: Understand what property patterns do

   Property patterns allow checking the values of properties inside an object directly in conditions.

2. Step 2: Identify the main use

   This helps write clearer and simpler code when you want to check multiple properties without nested ifs.

3. Final Answer:

   To check multiple properties of an object in a clear and concise way -> Option C

4. Quick Check:

   Property patterns simplify property checks = B [OK]

Hint: Property patterns simplify checking object properties [OK]

Common Mistakes:

• Confusing property patterns with property declaration
• Thinking property patterns create objects
• Assuming property patterns override methods

2. Which of the following is the correct syntax to use a property pattern in a switch expression for an object person with a property Age?

easy

A. case (Age > 18):

B. case { Age: > 18 }:

C. case Age > 18:

D. case person.Age > 18:

Solution

1. Step 1: Recall property pattern syntax

   Property patterns use curly braces with property name and condition inside, like { Age: > 18 }.

2. Step 2: Match with options

   case { Age: > 18 }: matches this syntax exactly, others use invalid or incorrect forms.

3. Final Answer:

   case { Age: > 18 }: -> Option B

4. Quick Check:

   Property pattern syntax uses braces = A [OK]

Hint: Use braces with property name and condition for property patterns [OK]

Common Mistakes:

• Using parentheses instead of braces
• Writing property condition without braces
• Referencing object name inside case

3. What will be the output of the following code?

record Person(string Name, int Age);

Person p = new("Alice", 25);

string result = p switch
{
    { Age: < 18 } => "Minor",
    { Age: >= 18 and < 65 } => "Adult",
    _ => "Senior"
};

Console.WriteLine(result);

medium

A. Adult

B. Minor

C. Senior

D. Compilation error

Solution

1. Step 1: Check the Age property of the Person object

   The person has Age = 25.

2. Step 2: Match Age with switch cases

   25 is not less than 18, so first case fails. 25 is >= 18 and < 65, so second case matches and returns "Adult".

3. Final Answer:

   Adult -> Option A

4. Quick Check:

   Age 25 fits adult range = A [OK]

Hint: Match property values carefully in switch cases [OK]

Common Mistakes:

• Confusing range conditions
• Assuming default case runs first
• Ignoring property pattern syntax

4. Identify the error in the following code using property patterns:

record Product(string Name, decimal Price);

Product p = new("Book", 15.99m);

if (p is { Price > 10 })
{
    Console.WriteLine("Expensive");
}

medium

A. The if statement requires parentheses around the pattern

B. The decimal literal should not have 'm' suffix

C. The record declaration is missing a semicolon

D. The property pattern syntax is incorrect; it should be { Price: > 10 }

Solution

1. Step 1: Check property pattern syntax

   Property patterns require a colon between property name and condition, like { Price: > 10 }.

2. Step 2: Identify the error in the code

   The code uses { Price > 10 } which is invalid syntax.

3. Final Answer:

   The property pattern syntax is incorrect; it should be { Price: > 10 } -> Option D

4. Quick Check:

   Property patterns need colon between property and condition = D [OK]

Hint: Use colon between property and condition in patterns [OK]

Common Mistakes:

• Omitting colon in property pattern
• Misunderstanding decimal literal suffix
• Adding unnecessary parentheses

5. Given a list of Person objects, how can you use property patterns in a switch expression to classify each person as "Child" if Age < 13, "Teen" if Age between 13 and 19, "Adult" if Age between 20 and 64, and "Senior" otherwise? Which code snippet correctly implements this?

hard

A. persons.Select(p => p switch { { Age: < 13 } => "Child", { Age: >= 13 and <= 19 } => "Teen", { Age: >= 20 and <= 64 } => "Adult", _ => "Senior" })

B. persons.Select(p => p switch { Age < 13 => "Child", Age >= 13 and Age <= 19 => "Teen", Age >= 20 and Age <= 64 => "Adult", _ => "Senior" })

C. persons.Select(p => p switch { { Age < 13 } => "Child", { Age >= 13 and Age <= 19 } => "Teen", { Age >= 20 and Age <= 64 } => "Adult", _ => "Senior" })

D. persons.Select(p => p switch { { Age: < 13 } => "Child", { Age: > 13 and < 20 } => "Teen", { Age: >= 20 and < 65 } => "Adult", _ => "Senior" })

Solution

1. Step 1: Understand correct property pattern syntax with ranges

   Property patterns use colon and conditions like { Age: < 13 } and combine with and for ranges.

2. Step 2: Check each option for correct syntax and ranges

   persons.Select(p => p switch { { Age: < 13 } => "Child", { Age: >= 13 and <= 19 } => "Teen", { Age: >= 20 and <= 64 } => "Adult", _ => "Senior" }) uses correct syntax and inclusive ranges matching the problem. persons.Select(p => p switch { Age < 13 => "Child", Age >= 13 and Age <= 19 => "Teen", Age >= 20 and Age <= 64 => "Adult", _ => "Senior" }) lacks braces and colons. persons.Select(p => p switch { { Age < 13 } => "Child", { Age >= 13 and Age <= 19 } => "Teen", { Age >= 20 and Age <= 64 } => "Adult", _ => "Senior" }) misplaces comparison operators inside braces. persons.Select(p => p switch { { Age: < 13 } => "Child", { Age: > 13 and < 20 } => "Teen", { Age: >= 20 and < 65 } => "Adult", _ => "Senior" }) uses exclusive Teen range (should include 13 and 19).

3. Final Answer:

   persons.Select(p => p switch { { Age: < 13 } => "Child", { Age: >= 13 and <= 19 } => "Teen", { Age: >= 20 and <= 64 } => "Adult", _ => "Senior" }) -> Option A

4. Quick Check:

   Correct property pattern syntax with proper ranges = C [OK]

Hint: Use braces and colon with 'and' for combined property conditions [OK]

Common Mistakes:

• Omitting braces or colon in property patterns
• Using incorrect range operators or missing boundaries
• Mixing syntax from other languages