Is-a relationship mental model in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method call in inheritance

What is the output of the following C# code that demonstrates the is-a relationship using inheritance?

C Sharp (C#)

class Animal {
    public virtual string Speak() {
        return "Animal sound";
    }
}

class Dog : Animal {
    public override string Speak() {
        return "Bark";
    }
}

class Program {
    static void Main() {
        Animal myPet = new Dog();
        System.Console.WriteLine(myPet.Speak());
    }
}

A Bark

B Compile-time error

C Runtime exception

D Animal sound

💡 Hint

Think about which method is called when a derived class overrides a base class method.

The variable myPet is of type Animal but refers to an instance of Dog. Because Speak() is overridden in Dog, the Dog's Speak() method is called, printing "Bark".

🧠 Conceptual

intermediate

Understanding the is-a relationship

Which statement best describes the is-a relationship in object-oriented programming?

A A class creates instances of other classes.

B A class contains another class as a member variable.

C A class implements multiple unrelated interfaces.

D A class inherits from another class, meaning it is a specialized type of that class.

💡 Hint

Think about inheritance and how one class relates to another as a type.

The is-a relationship means one class is a subtype of another through inheritance, showing a specialized version of the base class.

❓ Predict Output

advanced

Output with casting and is-a relationship

What will be the output of this C# program that uses casting and the is-a relationship?

C Sharp (C#)

class Vehicle {
    public virtual string Describe() => "Vehicle";
}

class Car : Vehicle {
    public override string Describe() => "Car";
}

class Program {
    static void Main() {
        Vehicle v = new Car();
        if (v is Car) {
            Car c = (Car)v;
            System.Console.WriteLine(c.Describe());
        } else {
            System.Console.WriteLine(v.Describe());
        }
    }
}

A Vehicle

B Invalid cast exception

C Car

D Compile-time error

💡 Hint

Check the type of the object before casting and which Describe method is called.

The variable v refers to a Car object, so the 'is' check passes. Casting to Car is safe, and the Car's Describe method returns "Car".

❓ Predict Output

advanced

Output of method hiding vs overriding

What is the output of this C# code demonstrating method hiding and the is-a relationship?

C Sharp (C#)

class Base {
    public string Show() => "Base Show";
}

class Derived : Base {
    public new string Show() => "Derived Show";
}

class Program {
    static void Main() {
        Base obj = new Derived();
        System.Console.WriteLine(obj.Show());
    }
}

A Runtime exception

B Base Show

C Compile-time error

D Derived Show

💡 Hint

Consider that method hiding does not override the base method.

The variable obj is of type Base, so the Base's Show method is called, even though the object is Derived. The new keyword hides the method but does not override it.

🧠 Conceptual

expert

Is-a relationship and interface implementation

Which statement correctly explains the is-a relationship when a class implements an interface in C#?

A Implementing an interface means the class is a subtype of the interface, establishing an is-a relationship.

B Implementing an interface creates a has-a relationship, not is-a.

C Interfaces cannot express is-a relationships in C#.

D A class implementing an interface must inherit from a base class to have an is-a relationship.

💡 Hint

Think about how interfaces define a contract that the class agrees to fulfill.

When a class implements an interface, it is considered a subtype of that interface, so it has an is-a relationship with the interface type.

Practice

1. What does the Is-a relationship represent in C# programming?

easy

A. A class contains another class as a member

B. A class inherits properties and methods from another class

C. A class is converted into another class

D. A class is unrelated to any other class

Solution

1. Step 1: Understand inheritance concept

   The Is-a relationship means one class inherits from another, gaining its features.

2. Step 2: Identify correct description

   A class inherits properties and methods from another class correctly describes inheritance, while others describe different concepts.

3. Final Answer:

   A class inherits properties and methods from another class -> Option B

4. Quick Check:

   Is-a means inheritance = B [OK]

Hint: Is-a means inheritance, not containment or conversion [OK]

Common Mistakes:

• Confusing Is-a with Has-a (containment)
• Thinking Is-a means type conversion
• Assuming unrelated classes have Is-a relationship

2. Which of the following is the correct syntax to express an Is-a relationship in C#?

easy

A. class Dog inherits Animal {}

B. class Dog extends Animal {}

C. class Dog : Animal {}

D. class Dog -> Animal {}

Solution

1. Step 1: Recall C# inheritance syntax

   In C#, the colon (:) symbol is used to indicate inheritance.

2. Step 2: Compare options

   class Dog : Animal {} uses the correct syntax 'class Dog : Animal {}'. Others use incorrect keywords or symbols.

3. Final Answer:

   class Dog : Animal {} -> Option C

4. Quick Check:

   C# inheritance uses ':' = C [OK]

Hint: Use ':' to inherit in C# classes [OK]

Common Mistakes:

• Using 'inherits' keyword (not valid in C#)
• Using 'extends' (Java syntax)
• Using arrows or other symbols

3. Consider this code:

class Animal { public string Speak() => "Sound"; } class Dog : Animal { }

What is the output of:

var d = new Dog(); Console.WriteLine(d.Speak());

medium

A. Runtime error

B. Dog

C. Compile error

D. Sound

Solution

1. Step 1: Understand inheritance effect

   Dog inherits from Animal, so Dog has the Speak() method.

2. Step 2: Predict method call output

   Calling d.Speak() returns "Sound" from Animal class.

3. Final Answer:

   Sound -> Option D

4. Quick Check:

   Inherited method returns "Sound" = A [OK]

Hint: Inherited methods can be called on child objects [OK]

Common Mistakes:

• Expecting Dog to override Speak() automatically
• Thinking code causes compile or runtime error
• Confusing output with class name

4. Identify the error in this code snippet:

class Animal { } class Dog Animal { }

medium

A. Missing colon ':' between Dog and Animal

B. Dog cannot inherit from Animal

C. Animal class must be abstract

D. Dog class must have a constructor

Solution

1. Step 1: Check inheritance syntax

   In C#, inheritance requires a colon ':' between child and parent class names.

2. Step 2: Identify missing symbol

   The code misses ':' between Dog and Animal, causing syntax error.

3. Final Answer:

   Missing colon ':' between Dog and Animal -> Option A

4. Quick Check:

   Inheritance needs ':' = A [OK]

Hint: Always use ':' to inherit in C# [OK]

Common Mistakes:

• Forgetting the colon ':'
• Thinking parent class must be abstract
• Assuming constructor is mandatory

5. Given these classes:

class Vehicle { public virtual string Move() => "Moving"; } class Car : Vehicle { public override string Move() => "Car is moving"; } class Bike : Vehicle { }

What will be the output of:

Vehicle v1 = new Car(); Vehicle v2 = new Bike(); Console.WriteLine(v1.Move()); Console.WriteLine(v2.Move());

hard

A. Car is moving\nMoving

B. Moving\nMoving

C. Car is moving\nBike is moving

D. Compile error due to missing override

Solution

1. Step 1: Understand virtual and override behavior

   Car overrides Move(), so v1.Move() calls Car's version. Bike does not override, so v2.Move() calls Vehicle's version.

2. Step 2: Predict output lines

   v1.Move() outputs "Car is moving"; v2.Move() outputs "Moving".

3. Final Answer:

   Car is moving\nMoving -> Option A

4. Quick Check:

   Override changes output, no override uses base = D [OK]

Hint: Override changes method output; no override uses base method [OK]

Common Mistakes:

• Expecting Bike to output 'Bike is moving'
• Thinking missing override causes compile error
• Confusing which method is called