Class declaration syntax in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic syntax to declare a class in C#?

Use the keyword <code>class</code> followed by the class name and curly braces. Example:<br><pre>class MyClass { }</pre>

beginner

What keyword is used to declare a class in C#?

The keyword class is used to declare a class.

beginner

Can a class in C# contain methods and variables?

Yes, a class can contain variables (fields) and methods (functions) inside its curly braces.

beginner

How do you declare a public class named <code>Car</code> in C#?

Use the <code>public</code> access modifier before the class keyword:<br><pre>public class Car { }</pre>

beginner

What is the purpose of curly braces <code>{ }</code> in a class declaration?

Curly braces define the body of the class where you put variables, methods, and other members.

Which keyword is used to declare a class in C#?

A class

B struct

C interface

D namespace

The class keyword declares a class in C#.

What symbol is used to enclose the body of a class?

A []

B ()

C {}

D <>

Curly braces { } enclose the class body.

How do you declare a class named Person that is accessible from other classes?

A public class Person { }

B class Person { }

C private class Person { }

D protected class Person { }

Use public to make the class accessible from other classes.

Which of these can be inside a class body?

A Only variables

B Variables and methods

C Only methods

D Nothing

Classes can contain both variables (fields) and methods.

What is the correct way to start a class declaration named Animal?

A class Animal[] {

B Animal class {

C class Animal() {

D class Animal {

The correct syntax is class Animal { followed by the class body.

Explain how to declare a simple class in C# including access modifier and body.

Think about the keywords and symbols you use to start and end a class.

Describe what can be included inside a class body in C#.

What parts make up the behavior and data of a class?

Practice

1. What is the correct way to declare a class named Car in C#?

easy

A. Car class { }

B. class Car { }

C. class = Car { }

D. class: Car { }

Solution

1. Step 1: Understand class declaration syntax

   In C#, a class is declared using the keyword class followed by the class name and curly braces.

2. Step 2: Match the correct syntax

   class Car { } uses class Car { }, which is the correct syntax for declaring a class named Car.

3. Final Answer:

   class Car { } -> Option B

4. Quick Check:

   Class declaration = class ClassName { } [OK]

Hint: Remember: class keyword + name + braces [OK]

Common Mistakes:

• Putting class name before keyword
• Using = or : instead of space
• Missing curly braces

2. Which of the following is a syntax error when declaring a class in C#?

easy

A. public class Person { }

B. class Animal { }

C. class 123Car { }

D. internal class House { }

Solution

1. Step 1: Check class name rules

   Class names must start with a letter or underscore, not a number.

2. Step 2: Identify invalid class name

   class 123Car { } uses class 123Car { }, which starts with digits, causing a syntax error.

3. Final Answer:

   class 123Car { } -> Option C

4. Quick Check:

   Class names cannot start with numbers [OK]

Hint: Class names must start with letter or underscore [OK]

Common Mistakes:

• Starting class name with a digit
• Using spaces in class name
• Using reserved keywords as class names

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

class Dog {
  public string Name = "Buddy";
}

class Program {
  static void Main() {
    Dog d = new Dog();
    System.Console.WriteLine(d.Name);
  }
}

medium

A. Buddy

B. Name

C. Dog

D. Compilation error

Solution

1. Step 1: Understand class field initialization

   The class Dog has a public field Name initialized to "Buddy".

2. Step 2: Trace the program output

   In Main, a Dog object is created and d.Name is printed, so output is "Buddy".

3. Final Answer:

   Buddy -> Option A

4. Quick Check:

   Field value printed = Buddy [OK]

Hint: Prints field value assigned in class [OK]

Common Mistakes:

• Confusing class name with field value
• Expecting method output instead of field
• Assuming compilation error without reason

4. Identify the error in this class declaration:

class Book
{
  string title;
  void SetTitle(string t)
  {
    title = t;
  }
}

medium

A. Missing access modifiers for field and method

B. Class name should be lowercase

C. Method SetTitle must return a value

D. Field title must be static

Solution

1. Step 1: Check access modifiers in class members

   By default, class members are private, but it's good practice to specify access modifiers explicitly.

2. Step 2: Identify missing access modifiers

   Field title and method SetTitle lack access modifiers like private or public, which can cause confusion or errors in some contexts.

3. Final Answer:

   Missing access modifiers for field and method -> Option A

4. Quick Check:

   Always specify access modifiers [OK]

Hint: Always add public/private to fields and methods [OK]

Common Mistakes:

• Assuming lowercase class names are required
• Thinking void methods must return a value
• Believing fields must be static

5. You want to create a class Student with a field name and a method GetName that returns the student's name. Which is the correct complete class declaration?

hard

A. class Student { public string name; public void GetName() { return name; } }

B. class Student { string name; string GetName() { name; } }

C. class Student { public string name; string GetName() { return name; } }

D. class Student { public string name; public string GetName() { return name; } }

Solution

1. Step 1: Check field and method access modifiers

   The field name and method GetName should be public to be accessible outside the class.

2. Step 2: Verify method return type and body

   GetName returns a string, so its return type must be string and it must return name.

3. Step 3: Identify correct option

   class Student { public string name; public string GetName() { return name; } } correctly declares name as public string and GetName as public string method returning name.

4. Final Answer:

   class Student { public string name; public string GetName() { return name; } } -> Option D

5. Quick Check:

   Public field + public string method returning field [OK]

Hint: Method return type must match returned value type [OK]

Common Mistakes:

• Missing return statement in method
• Wrong method return type (void instead of string)
• Missing public keyword for accessibility