Auto-implemented properties in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of auto-implemented property usage

What is the output of this C# code snippet using auto-implemented properties?

C Sharp (C#)

public class Person {
    public string Name { get; set; }
}

var p = new Person();
p.Name = "Alice";
System.Console.WriteLine(p.Name);

A Name

B null

C Alice

D Compilation error

💡 Hint

Auto-implemented properties automatically create a hidden field to store the value.

The property Name is auto-implemented with get and set. Assigning "Alice" to p.Name stores it, so printing p.Name outputs "Alice".

🧠 Conceptual

intermediate

Default value of auto-implemented property

What is the default value of an auto-implemented property of type int in C# if not explicitly set?

A null

B 0

C 1

D Compilation error

💡 Hint

Consider the default value of value types in C#.

Auto-implemented properties use backing fields. For int, the default value is 0 if not set.

🔧 Debug

advanced

Identify the error in auto-implemented property declaration

What error does this code produce? public class Car { public string Model { get; } } var c = new Car(); c.Model = "Tesla";

C Sharp (C#)

public class Car {
    public string Model { get; }
}

var c = new Car();
c.Model = "Tesla";

A CS0200: Property or indexer 'Car.Model' cannot be assigned to -- it is read only

B CS0120: An object reference is required for the non-static field, method, or property

C No error, outputs Tesla

D CS0501: 'Car.Model.set' must declare a body because it is not marked abstract or extern

💡 Hint

Check if the property has a setter.

The property Model has only a getter, so assigning to it causes a compile-time error CS0200.

📝 Syntax

advanced

Correct syntax for auto-implemented property with private setter

Which option correctly declares an auto-implemented property named Age with a public getter and a private setter?

A public int Age { get private; set; }

B public int Age { private get; set; }

C public int Age { get; set; private }

D public int Age { get; private set; }

💡 Hint

The access modifier for the setter goes before 'set;' inside the property.

Option D uses the correct syntax for a private setter with a public getter.

🚀 Application

expert

Number of items in dictionary from auto-implemented property usage

Consider this C# code: public class Item { public int Id { get; set; } } var items = new List { new Item { Id = 1 }, new Item { Id = 2 }, new Item { Id = 1 } }; var dict = items.ToDictionary(i => i.Id); How many items does dict contain after execution?

C Sharp (C#)

public class Item {
    public int Id { get; set; }
}

var items = new List<Item> {
    new Item { Id = 1 },
    new Item { Id = 2 },
    new Item { Id = 1 }
};

var dict = items.ToDictionary(i => i.Id);

System.Console.WriteLine(dict.Count);

A Runtime exception

B 3

C 1

D 2

💡 Hint

Check if keys in a dictionary must be unique.

The ToDictionary method throws an exception because there are duplicate keys (Id=1) in the list.

Practice

1. What is the main advantage of using auto-implemented properties in C#?

easy

A. They replace constructors for initializing objects.

B. They allow methods to be called without creating an object.

C. They automatically create a private backing field without extra code.

D. They enable multiple inheritance in classes.

Solution

1. Step 1: Understand what auto-implemented properties do

   Auto-implemented properties create a hidden private field automatically to store data without writing extra code.

2. Step 2: Compare with other options

   Options A, B, and C describe unrelated features: constructors, method calls, and inheritance, which are not related to auto-implemented properties.

3. Final Answer:

   They automatically create a private backing field without extra code. -> Option C

4. Quick Check:

   Auto-implemented properties = hidden backing field [OK]

Hint: Auto-properties hide the field; no manual variable needed [OK]

Common Mistakes:

• Confusing properties with methods
• Thinking auto-properties replace constructors
• Believing they enable inheritance

2. Which of the following is the correct syntax for an auto-implemented property named Age of type int?

easy

A. public int Age { get; set; }

B. public int Age() { get; set; }

C. public int Age { get get; set; }

D. public int Age get; set;

Solution

1. Step 1: Identify correct property syntax

   The correct syntax for an auto-implemented property uses curly braces with get; and set; inside: public int Age { get; set; }.

2. Step 2: Check other options for syntax errors

   public int Age() { get; set; } uses parentheses which are for methods, not properties. public int Age { get get; set; } repeats get incorrectly. public int Age get; set; misses braces and semicolons are misplaced.

3. Final Answer:

   public int Age { get; set; } -> Option A

4. Quick Check:

   Property syntax = { get; set; } [OK]

Hint: Properties use braces { } with get; and set; inside [OK]

Common Mistakes:

• Using parentheses instead of braces
• Writing get or set twice
• Omitting braces or semicolons

3. What will be the output of this C# code?

class Person {
    public string Name { get; set; }
}

var p = new Person();
p.Name = "Alice";
Console.WriteLine(p.Name);

medium

A. null

B. Alice

C. Name

D. Compilation error

Solution

1. Step 1: Understand property assignment

   The property Name is auto-implemented, so it stores the value "Alice" when assigned.

2. Step 2: Output the property value

   When Console.WriteLine(p.Name); runs, it prints the stored string "Alice".

3. Final Answer:

   Alice -> Option B

4. Quick Check:

   Property stores "Alice" = output "Alice" [OK]

Hint: Auto-properties store and return assigned values [OK]

Common Mistakes:

• Expecting property name instead of value
• Thinking default null prints as text
• Assuming syntax error without reason

4. Identify the error in this code snippet:

class Car {
    public int Speed { get; private set; }
}

var c = new Car();
c.Speed = 100;
Console.WriteLine(c.Speed);

medium

A. No error; code runs and prints 100.

B. Missing semicolon after property declaration.

C. Property 'Speed' must be static.

D. Cannot assign to 'Speed' because the setter is private.

Solution

1. Step 1: Analyze property access modifiers

   The property Speed has a private setter, so it cannot be assigned outside the class.

2. Step 2: Check assignment in main code

   The line c.Speed = 100; tries to assign from outside, causing a compile error.

3. Final Answer:

   Cannot assign to 'Speed' because the setter is private. -> Option D

4. Quick Check:

   Private setter blocks external assignment [OK]

Hint: Private set means only class can assign property [OK]

Common Mistakes:

• Ignoring setter access level
• Assuming public setter by default
• Confusing property with field

5. You want to create a class Book with an auto-implemented property Title that can be read publicly but only set privately within the class. Which code snippet correctly implements this?

hard

A. public class Book { public string Title { get; private set; } }

B. public class Book { private string Title { get; set; } }

C. public class Book { public string Title { private get; set; } }

D. public class Book { public string Title { get; set; private } }

Solution

1. Step 1: Understand access modifiers for properties

   To allow public reading but private setting, the getter must be public and setter private: get; private set;.

2. Step 2: Check each option's syntax and access

   public class Book { public string Title { get; private set; } } correctly uses public string Title { get; private set; }. public class Book { private string Title { get; set; } } makes the whole property private. public class Book { public string Title { private get; set; } } incorrectly places private before get. public class Book { public string Title { get; set; private } } has invalid syntax.

3. Final Answer:

   public class Book { public string Title { get; private set; } } -> Option A

4. Quick Check:

   Public get + private set = public class Book { public string Title { get; private set; } } [OK]

Hint: Use 'get; private set;' for public read, private write [OK]

Common Mistakes:

• Placing private before get instead of set
• Making whole property private
• Incorrect syntax order for accessors