Record structs in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a record struct named Point with two integer properties X and Y.

C Sharp (C#)

public [1] Point(int X, int Y);

Drag options to blanks, or click blank then click option'

Aclass

Bstruct

Crecord struct

Drecord class

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' or 'record class' instead of 'record struct'.

Using just 'struct' which is not a record struct.

The keyword record struct declares a record struct in C# which is a value type with built-in value equality.

2fill in blank

medium

Complete the code to create a new Point record struct instance with X=5 and Y=10.

C Sharp (C#)

var p = new Point([1], 10);

Drag options to blanks, or click blank then click option'

A5

BX

CY

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using the property name 'X' instead of the value 5.

Using 10 for the first parameter instead of the second.

When creating a new instance, you provide the values for the parameters. Here, X is 5.

3fill in blank

hard

Fix the error in the code to correctly compare two Point record structs for equality.

C Sharp (C#)

bool areEqual = p1 [1] p2;

Drag options to blanks, or click blank then click option'

Aequals

B==

C!=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which is assignment, not comparison.

Using 'equals' which is not a valid operator in C#.

Record structs support value equality with the == operator.

4fill in blank

hard

Fill both blanks to declare a record struct named Rectangle with properties Width and Height.

C Sharp (C#)

public [1] Rectangle(int [2], int Height);

Drag options to blanks, or click blank then click option'

Arecord struct

Bclass

CWidth

DHeight

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of 'record struct'.

Using 'Height' instead of 'Width' for the first parameter.

The declaration uses 'record struct' and the first parameter name is 'Width'.

5fill in blank

hard

Fill all three blanks to create a new Rectangle instance with Width=15 and Height=25, then check if Width is greater than 10.

C Sharp (C#)

var rect = new Rectangle([1], [2]);
bool isWide = rect.Width [3] 10;

Drag options to blanks, or click blank then click option'

A15

B25

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping Width and Height values.

Using '<' instead of '>' for the comparison.

The Rectangle is created with Width=15 and Height=25. The comparison checks if Width is greater than 10.

Practice

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

easy

A. It provides value-based equality and immutability by default.

B. It allows inheritance from other structs.

C. It can only be used for reference types.

D. It does not support property declarations.

Solution

1. Step 1: Understand record struct purpose

   Record structs combine struct's lightweight nature with record's value-based equality and immutability.

2. Step 2: Analyze options

   It provides value-based equality and immutability by default. correctly states value-based equality and immutability. Options B, C, and D are incorrect because structs cannot inherit, record structs are value types, and they support properties.

3. Final Answer:

   It provides value-based equality and immutability by default. -> Option A

4. Quick Check:

   record struct = value equality + immutability [OK]

Hint: Remember: record structs behave like immutable value containers [OK]

Common Mistakes:

• Thinking record structs support inheritance
• Confusing record structs with classes
• Assuming record structs are reference types

2. Which of the following is the correct syntax to declare a record struct named Point with two properties X and Y of type int?

easy

A. struct record Point { int X; int Y; }

B. record Point struct { int X; int Y; }

C. record struct Point(int X, int Y);

D. record struct Point { int X; int Y; }

Solution

1. Step 1: Recall record struct declaration syntax

   The concise syntax for record structs uses positional parameters: record struct Name(type prop1, type prop2);

2. Step 2: Compare options

   record struct Point(int X, int Y); matches the correct syntax. record struct Point { int X; int Y; } is close but missing parentheses for positional parameters. Options A and C have incorrect order or keywords.

3. Final Answer:

   record struct Point(int X, int Y); -> Option C

4. Quick Check:

   record struct with positional params = record struct Point(int X, int Y); [OK]

Hint: Use parentheses for positional properties in record structs [OK]

Common Mistakes:

• Swapping 'record' and 'struct' keywords
• Omitting parentheses for positional parameters
• Using braces instead of parentheses for positional syntax

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

record struct 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 equality in record structs

   Record structs provide value-based equality by default, so two instances with same values are equal.

2. Step 2: Analyze the code output

   Both p1 and p2 have X=3 and Y=4, so p1 == p2 evaluates to true.

3. Final Answer:

   True -> Option A

4. Quick Check:

   record struct equality = value equality [OK]

Hint: Record structs compare values, not references [OK]

Common Mistakes:

• Assuming == compares references for structs
• Expecting compilation error for == operator
• Confusing record structs with classes for equality

4. Identify the error in this code snippet:

record struct Rectangle(int Width, int Height);
var rect = new Rectangle(5, 10);
rect.Width = 7;
Console.WriteLine(rect);

medium

A. Rectangle must be a class to allow property assignment.

B. Missing semicolon after record struct declaration.

C. Console.WriteLine cannot print record structs.

D. Cannot assign to 'Width' because it is readonly.

Solution

1. Step 1: Understand immutability of record structs

   Record structs with positional parameters generate readonly properties by default.

2. Step 2: Analyze the assignment line

   Trying to assign rect.Width = 7; causes a compile-time error because Width is readonly.

3. Final Answer:

   Cannot assign to 'Width' because it is readonly. -> Option D

4. Quick Check:

   Positional record struct properties are readonly [OK]

Hint: Positional record struct properties are readonly by default [OK]

Common Mistakes:

• Trying to modify readonly properties
• Confusing record structs with mutable classes
• Ignoring compiler error messages

5. You want to create a lightweight data type to store a 3D point with coordinates X, Y, and Z. You want it to be immutable, support value equality, and print nicely. Which is the best way to declare it using record structs?

hard

A. struct Point3D { public int X; public int Y; public int Z; }

B. record struct Point3D(int X, int Y, int Z);

C. class Point3D { public int X { get; set; } public int Y { get; set; } public int Z { get; set; } }

D. record class Point3D(int X, int Y, int Z);

Solution

1. Step 1: Identify requirements

   Needs lightweight, immutable, value equality, and nice printing.

2. Step 2: Match requirements to options

   record struct Point3D(int X, int Y, int Z); uses record struct with positional parameters, providing all requirements. struct Point3D { public int X; public int Y; public int Z; } is mutable struct without value equality or nice printing. class Point3D { public int X { get; set; } public int Y { get; set; } public int Z { get; set; } } is mutable class, heavier and reference type. record class Point3D(int X, int Y, int Z); is record class, reference type, not lightweight.

3. Final Answer:

   record struct Point3D(int X, int Y, int Z); -> Option B

4. Quick Check:

   record struct = lightweight + immutable + value equality [OK]

Hint: Use record struct with positional params for immutable lightweight data [OK]

Common Mistakes:

• Choosing class instead of struct for lightweight data
• Using mutable fields instead of readonly properties
• Confusing record class with record struct