Record declaration syntax in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple record declaration

What is the output of this C# program using a record declaration?

C Sharp (C#)

public record Person(string Name, int Age);

class Program {
    static void Main() {
        var p = new Person("Alice", 30);
        System.Console.WriteLine(p);
    }
}

A Name: Alice, Age: 30

B Alice 30

C Person(Alice, 30)

D Person { Name = Alice, Age = 30 }

💡 Hint

Records override ToString() to show property names and values.

In C#, records automatically generate a ToString() method that outputs the record type name and its properties with their values in the format: TypeName { Property1 = value1, Property2 = value2 }.

❓ Predict Output

intermediate

Output of record with inheritance

What is the output of this C# program with record inheritance?

C Sharp (C#)

public record Animal(string Name);
public record Dog(string Name, string Breed) : Animal(Name);

class Program {
    static void Main() {
        var d = new Dog("Buddy", "Beagle");
        System.Console.WriteLine(d);
    }
}

A Dog { Name = Buddy, Breed = Beagle }

B Animal { Name = Buddy }

C Dog(Buddy, Beagle)

D Buddy Beagle

💡 Hint

Derived records include all properties in ToString output.

The derived record Dog inherits from Animal and adds Breed. The ToString() method shows all properties from both records.

🔧 Debug

advanced

Identify the syntax error in record declaration

Which option contains a syntax error in the record declaration?

A public record Car(string Make; string Model);

B public record Car(string Make, string Model);

C public record Car(string Make, string Model) {}

D public record Car { string Make; string Model; }

💡 Hint

Check the separator between parameters in the record declaration.

In C#, record positional parameters must be separated by commas, not semicolons. Option A uses semicolons, causing a syntax error.

❓ Predict Output

advanced

Output of record with custom ToString override

What is the output of this C# program with a record that overrides ToString()?

C Sharp (C#)

public record Point(int X, int Y) {
    public override string ToString() => $"({X}, {Y})";
}

class Program {
    static void Main() {
        var pt = new Point(3, 4);
        System.Console.WriteLine(pt);
    }
}

A 3, 4

B Point { X = 3, Y = 4 }

C (3, 4)

D Point(3, 4)

💡 Hint

The record overrides ToString to return a custom string.

The overridden ToString() method returns the coordinates in parentheses, so the output is (3, 4).

🧠 Conceptual

expert

Number of properties in a record with inheritance

Given these record declarations, how many properties does the record 'Employee' have?

C Sharp (C#)

public record Person(string Name, int Age);
public record Employee(string Name, int Age, string Position) : Person(Name, Age);

A 2

B 3

C 4

D 1

💡 Hint

Count all positional parameters from base and derived records.

Employee inherits Name and Age from Person and adds Position, so it has 3 properties total.

Practice

1. What is a key feature of a record in C#?

easy

A. It provides immutable data with value-based equality.

B. It allows mutable fields by default.

C. It is used only for database connections.

D. It cannot have properties.

Solution

1. Step 1: Understand what a record is

   A record is a special type in C# designed to hold data immutably.

2. Step 2: Identify the main feature

   Records compare by value, not by reference, and are immutable by default.

3. Final Answer:

   It provides immutable data with value-based equality. -> Option A

4. Quick Check:

   Record = Immutable + Value Equality [OK]

Hint: Remember: records are immutable and compare by value [OK]

Common Mistakes:

• Thinking records are mutable by default
• Confusing records with classes for database use
• Believing records cannot have properties

2. Which of the following is the correct syntax to declare a record with two properties int Id and string Name?

easy

A. record Person { int Id; string Name; }

B. record Person(int Id, string Name);

C. record Person = (int Id, string Name);

D. record Person(int Id; string Name);

Solution

1. Step 1: Recall record declaration syntax

   Records use parentheses with comma-separated parameters for properties.

2. Step 2: Check each option

   record Person(int Id, string Name); uses correct syntax: parentheses and commas. record Person { int Id; string Name; } uses braces without property syntax. record Person = (int Id, string Name); uses '=' incorrectly. record Person(int Id; string Name); uses semicolon instead of comma.

3. Final Answer:

   record Person(int Id, string Name); -> Option B

4. Quick Check:

   Record syntax = parentheses + commas [OK]

Hint: Use parentheses with commas for record properties [OK]

Common Mistakes:

• Using braces instead of parentheses
• Using semicolons instead of commas
• Adding '=' sign incorrectly

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

record Point(int X, int Y);
var p1 = new Point(3, 4);
var p2 = new Point(3, 4);
Console.WriteLine(p1 == p2);

medium

A. True

B. False

C. Compilation error

D. Runtime exception

Solution

1. Step 1: Understand record equality behavior

   Records compare by value, so two records with same property values are equal.

2. Step 2: Analyze the code

   p1 and p2 have same X and Y values (3,4), so p1 == p2 returns true.

3. Final Answer:

   True -> Option A

4. Quick Check:

   Records compare by value = True [OK]

Hint: Records compare by value, so identical values mean equality [OK]

Common Mistakes:

• Assuming reference equality instead of value equality
• Expecting false because of different instances
• Thinking it causes a compilation error

4. Identify the error in this record declaration:

record Car(string Make, string Model)
{
    public int Year;
}

medium

A. Records cannot have any fields declared inside braces.

B. The semicolon is missing after the record declaration.

C. The record must use parentheses for properties, not braces.

D. Fields inside records must be declared as properties, not fields.

Solution

1. Step 1: Understand record members

   Records can have members, but fields should be properties for immutability.

2. Step 2: Analyze the code

   The code declares a public field 'Year' instead of a property, which is not recommended and causes issues.

3. Final Answer:

   Fields inside records must be declared as properties, not fields. -> Option D

4. Quick Check:

   Use properties, not fields inside records [OK]

Hint: Use properties, not fields, inside records for immutability [OK]

Common Mistakes:

• Using fields instead of properties inside records
• Missing semicolon after record declaration (not required here)
• Confusing braces and parentheses usage

5. You want to declare a record Book with properties string Title, string Author, and an optional int? Year that defaults to null. Which is the correct way to declare it?

hard

A. record Book { string Title; string Author; int? Year = null; }

B. record Book(string Title, string Author, int? Year);

C. record Book(string Title, string Author, int? Year = null);

D. record Book(string Title, string Author) { public int? Year = null; }

Solution

1. Step 1: Use concise record syntax with default parameter

   Records allow default values in the parameter list using '='.

2. Step 2: Check each option

   record Book(string Title, string Author, int? Year = null); correctly declares Year as nullable with default null. record Book(string Title, string Author, int? Year); lacks default. record Book { string Title; string Author; int? Year = null; } uses invalid field syntax. record Book(string Title, string Author) { public int? Year = null; } uses field with default inside braces, which is not idiomatic.

3. Final Answer:

   record Book(string Title, string Author, int? Year = null); -> Option C

4. Quick Check:

   Default values go in parentheses parameters [OK]

Hint: Set default values inside parentheses in record declarations [OK]

Common Mistakes:

• Omitting default value for optional parameters
• Using fields instead of properties inside braces
• Trying to assign default values inside braces