Types of inheritance in C++ - Step-by-Step Execution

Concept Flow - Types of inheritance

Base Class

↓

Single Inheritance

↓

Base Class

↓

Derived1

↓

Multiple Inheritance

↓

Base1

↓

Derived

↓

Base

↓

Derived1

↓

Derived2

↓

Base

↓

Derived1

↓

Derived2

↓

Derived3

Shows how classes inherit from one or more base classes in different ways: single, multiple, multilevel, hierarchical, and hybrid inheritance.

Execution Sample

C++

class Base {
public:
  int x = 10;
};

class Derived : public Base {
public:
  int y = 20;
};

Defines a base class with a variable and a derived class that inherits it and adds another variable.

Execution Table

Step	Action	Class	Variable Accessed	Value	Explanation
1	Create Base object	Base	x	10	Base class object has x=10
2	Create Derived object	Derived	x	10	Derived inherits x from Base
3	Access Derived.y	Derived	y	20	Derived class own variable y=20
4	Access Derived.x	Derived	x	10	Derived accesses inherited x=10
5	End	-	-	-	Execution ends

💡 All variables accessed and inheritance verified, program ends.

Variable Tracker

Variable	Base Object	Derived Object
x	10	10
y	-	20

Key Moments - 3 Insights

Why can Derived access variable x even though it is declared in Base?

Because Derived inherits from Base, it gets all public members like x. See execution_table row 4 where Derived.x is 10.

What happens if we create an object of Base and try to access y?

Base does not have y, so accessing y on Base object is invalid. See execution_table row 1 where only x exists.

How does multiple inheritance differ from single inheritance?

Multiple inheritance means a class inherits from more than one base class, combining their members. Single inheritance inherits from only one base class.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x in the Derived object at step 4?

A 10

B 20

C 0

D Undefined

💡 Hint

Check execution_table row 4 where Derived.x is accessed.

At which step does the Derived object get its own variable y initialized?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at execution_table row 3 where Derived.y is accessed.

If we add another base class and inherit from both, what type of inheritance is this?

A Single inheritance

B Multiple inheritance

C Multilevel inheritance

D Hierarchical inheritance

💡 Hint

Refer to concept_flow diagram showing multiple inheritance with two base classes.

Concept Snapshot

Types of inheritance in C++:
- Single: One base, one derived.
- Multiple: One derived, multiple bases.
- Multilevel: Chain of inheritance.
- Hierarchical: One base, many derived.
- Hybrid: Combination of above.
Derived classes inherit members from base classes.

Full Transcript

This visual execution shows different types of inheritance in C++. We start with a base class having a variable x. A derived class inherits from it and adds variable y. The execution table traces creating objects and accessing variables, showing how inheritance works. Key moments clarify why derived classes can access base members and differences between inheritance types. The quiz tests understanding of variable values and inheritance types. The concept snapshot summarizes the main inheritance types and their behavior.

Practice

1. Which type of inheritance involves a single derived class inheriting from one base class in C++?

easy

A. Hierarchical inheritance

B. Multiple inheritance

C. Multilevel inheritance

D. Single inheritance

Solution

1. Step 1: Understand inheritance types

   Single inheritance means one class inherits from exactly one base class.

2. Step 2: Match definition to options

   Only Single inheritance describes a single derived class inheriting from one base class.

3. Final Answer:

   Single inheritance -> Option D

4. Quick Check:

   One derived, one base = Single inheritance [OK]

Hint: One derived from one base is single inheritance [OK]

Common Mistakes:

• Confusing multiple inheritance with single inheritance
• Thinking multilevel means one base class only
• Mixing hierarchical with single inheritance

2. Which of the following is the correct syntax for multiple inheritance in C++?

easy

A. class Derived : public Base1 & Base2 {};

B. class Derived : public Base1, public Base2 {};

C. class Derived : Base1 Base2 {};

D. class Derived inherits Base1, Base2 {};

Solution

1. Step 1: Recall multiple inheritance syntax

   In C++, multiple inheritance uses commas to separate base classes with access specifiers.

2. Step 2: Check each option

   class Derived : public Base1, public Base2 {}; uses correct syntax: 'class Derived : public Base1, public Base2 {};'. Others have syntax errors.

3. Final Answer:

   class Derived : public Base1, public Base2 {}; -> Option B

4. Quick Check:

   Comma separates base classes with access specifiers [OK]

Hint: Use commas and access specifiers for multiple inheritance [OK]

Common Mistakes:

• Omitting commas between base classes
• Using '&' instead of commas
• Writing 'inherits' keyword which doesn't exist in C++

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

class A { public: void show() { std::cout << "A"; } };
class B : public A { public: void show() { std::cout << "B"; } };
class C : public B {};
int main() {
  C obj;
  obj.show();
  return 0;
}

medium

A. B

B. A

C. C

D. Compilation error

Solution

1. Step 1: Understand inheritance chain

   Class C inherits from B, which inherits from A. B overrides show() method.

2. Step 2: Determine which show() is called

   Calling obj.show() on C calls B's show() because C inherits B's version and does not override it.

3. Final Answer:

   B -> Option A

4. Quick Check:

   Derived class method called if overridden [OK]

Hint: Derived class method overrides base method unless not overridden [OK]

Common Mistakes:

• Assuming base class method runs instead of overridden
• Expecting 'C' output though C has no show()
• Thinking code causes compilation error

4. Identify the error in this C++ code snippet involving inheritance:

class Base { public: int x; };
class Derived : Base {};
int main() {
  Derived d;
  d.x = 1;
  return 0;
}

medium

A. Main function missing return type

B. Base class must be declared inside Derived

C. Missing access specifier before Base in Derived class

D. Derived class cannot be empty

Solution

1. Step 1: Check inheritance syntax

   In C++, inheritance requires an access specifier like public, private, or protected before base class name.

2. Step 2: Identify the error

   Derived : Base {} lacks access specifier; should be Derived : public Base {}.

3. Final Answer:

   Missing access specifier before Base in Derived class -> Option C

4. Quick Check:

   Inheritance needs access specifier [OK]

Hint: Always specify public/private/protected before base class [OK]

Common Mistakes:

• Omitting access specifier in inheritance
• Thinking empty class body is error
• Confusing return type in main function

5. Given the following classes:

class Animal { public: void eat() { std::cout << "Eating"; } };
class Mammal : public Animal {};
class Bird : public Animal {};
class Bat : public Mammal, public Bird {};
int main() {
  Bat b;
  b.eat();
  return 0;
}

What problem arises and how to fix it?

hard

A. Ambiguity error due to multiple inheritance; fix with virtual inheritance

B. No problem; code runs fine

C. Syntax error in Bat class declaration

D. eat() method must be overridden in Bat

Solution

1. Step 1: Analyze inheritance structure

   Bat inherits Mammal and Bird, both inherit Animal, causing two Animal copies in Bat.

2. Step 2: Identify ambiguity

   Calling b.eat() is ambiguous because Bat has two Animal parts; compiler error occurs.

3. Step 3: Fix with virtual inheritance

   Use virtual inheritance for Mammal and Bird from Animal to share one Animal base.

4. Final Answer:

   Ambiguity error due to multiple inheritance; fix with virtual inheritance -> Option A

5. Quick Check:

   Diamond problem fixed by virtual inheritance [OK]

Hint: Use virtual inheritance to solve diamond ambiguity [OK]

Common Mistakes:

• Ignoring diamond problem ambiguity
• Thinking code compiles without error
• Assuming method override fixes ambiguity