Constructor overloading in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a constructor that takes no arguments.

C++

class Box {
public:
    Box() [1] {}
};

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

Areturn

Bvoid

C: width(0), height(0), depth(0)

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to put a return type for the constructor.

Using 'void' keyword in constructor declaration.

The constructor initializes width, height, and depth to 0 using an initializer list.

2fill in blank

medium

Complete the code to declare a constructor that takes three integer parameters.

C++

class Box {
public:
    Box(int w, int h, int d) [1] {}
};

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

Areturn w, h, d;

Bwidth = w; height = h; depth = d;

Cvoid

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to use 'return' inside constructor.

Adding a return type like 'void' or 'int' to constructor.

The constructor assigns the parameters to the class members inside the constructor body.

3fill in blank

hard

Fix the error in the constructor declaration to properly overload it.

C++

class Box {
public:
    Box() {}
    Box(int w, int h, int d) [1] {}
};

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

ABox()

BBox(int w, int h)

Cvoid Box(int w, int h, int d)

DBox(int w, int h, int d)

Attempts:

3 left

💡 Hint

Common Mistakes

Adding a return type like 'void' to constructor.

Changing the constructor name to something else.

The constructor must have the same name as the class and no return type to overload properly.

4fill in blank

hard

Fill both blanks to complete the constructor initializer list and body.

C++

class Box {
    int width, height, depth;
public:
    Box(int w, int h, int d) [1] [2] {}
};

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

A: width(w), height(h), depth(d)

Bwidth = w; height = h; depth = d;

C{}

D;

Attempts:

3 left

💡 Hint

Common Mistakes

Putting assignments inside the initializer list.

Forgetting the colon before initializer list.

The initializer list sets the members before the constructor body, which is empty here.

5fill in blank

hard

Fill all three blanks to complete the overloaded constructors with default values.

C++

class Box {
    int width, height, depth;
public:
    Box() [1] {}
    Box(int w) [2] {}
    Box(int w, int h, int d) [3] {}
};

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

A: width(0), height(0), depth(0)

B: width(w), height(0), depth(0)

C: width(w), height(h), depth(d)

Dwidth = 0; height = 0; depth = 0;

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to assign values inside the constructor body instead of initializer list.

Forgetting to initialize all members.

Each constructor uses an initializer list to set member variables with appropriate default or given values.

Practice

1. What is constructor overloading in C++?

easy

A. Creating constructors only with no parameters

B. Having multiple constructors with different parameters in the same class

C. Using the same constructor multiple times in a program

D. Defining constructors outside the class only

Solution

1. Step 1: Understand constructor overloading concept

   Constructor overloading means having more than one constructor in a class, each with different parameters.

2. Step 2: Match definition with options

   Having multiple constructors with different parameters in the same class correctly describes this concept, while others describe unrelated ideas.

3. Final Answer:

   Having multiple constructors with different parameters in the same class -> Option B

4. Quick Check:

   Constructor overloading = multiple constructors with different parameters [OK]

Hint: Look for multiple constructors with different parameter lists [OK]

Common Mistakes:

• Confusing overloading with overriding
• Thinking constructors must have no parameters
• Believing constructors can only be defined outside the class

2. Which of the following is the correct syntax for constructor overloading in C++?

easy

A. class MyClass { MyClass(); MyClass(int x); };

B. class MyClass { void MyClass(); void MyClass(int x); };

C. class MyClass { int MyClass(); int MyClass(int x); };

D. class MyClass { MyClass() int x; MyClass(int x) int x; };

Solution

1. Step 1: Check constructor syntax

   Constructors have no return type and share the class name.

2. Step 2: Identify correct syntax

   class MyClass { MyClass(); MyClass(int x); }; shows constructors with no return type and different parameters, which is correct. Others wrongly use return types or invalid syntax.

3. Final Answer:

   class MyClass { MyClass(); MyClass(int x); }; -> Option A

4. Quick Check:

   Constructors have no return type [OK]

Hint: Remember constructors have no return type, just the class name [OK]

Common Mistakes:

• Adding return types to constructors
• Using void or int before constructor name
• Incorrect punctuation or missing semicolons

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

class Box {
public:
  int length;
  Box() { length = 5; }
  Box(int l) { length = l; }
};

int main() {
  Box b1;
  Box b2(10);
  std::cout << b1.length << " " << b2.length;
  return 0;
}

medium

A. 5 5

B. 0 10

C. 5 10

D. 10 5

Solution

1. Step 1: Identify which constructor is called for each object

   b1 uses the default constructor setting length to 5; b2 uses the parameterized constructor setting length to 10.

2. Step 2: Determine output from std::cout

   Output prints b1.length (5) and b2.length (10) separated by space.

3. Final Answer:

   5 10 -> Option C

4. Quick Check:

   Default constructor sets 5, parameterized sets 10 [OK]

Hint: Match constructor parameters with object creation [OK]

Common Mistakes:

• Assuming uninitialized variables default to 0
• Mixing up which constructor is called
• Forgetting to print both values

4. Find the error in this constructor overloading example:

class Sample {
public:
  Sample() { }
  Sample() { }
};

medium

A. Two constructors have the same parameter list causing a redefinition error

B. Constructors must have return type

C. Constructors cannot be public

D. Class must have at least one data member

Solution

1. Step 1: Check constructor signatures

   Both constructors have no parameters, so they have identical signatures.

2. Step 2: Understand C++ rules on overloading

   Constructors must differ in parameter lists to overload; identical signatures cause redefinition error.

3. Final Answer:

   Two constructors have the same parameter list causing a redefinition error -> Option A

4. Quick Check:

   Constructor signatures must differ [OK]

Hint: Overloaded constructors must differ in parameters [OK]

Common Mistakes:

• Trying to overload with same parameter list
• Adding return types to constructors
• Thinking constructors can't be public

5. Given the class below, which constructor will be called when creating MyClass obj(3.14);?

class MyClass {
public:
  MyClass(int x) { std::cout << "Int constructor"; }
  MyClass(double x) { std::cout << "Double constructor"; }
  MyClass(float x) { std::cout << "Float constructor"; }
};

hard

A. Compilation error due to ambiguity

B. Int constructor

C. Float constructor

D. Double constructor

Solution

1. Step 1: Identify argument type in object creation

   3.14 is a double literal by default in C++.

2. Step 2: Match argument type to constructor

   The constructor with double parameter matches exactly, so it is called.

3. Final Answer:

   Double constructor -> Option D

4. Quick Check:

   Exact type match constructor is chosen [OK]

Hint: Literal 3.14 is double by default, so double constructor called [OK]

Common Mistakes:

• Assuming float constructor is called for 3.14
• Thinking int constructor is called due to truncation
• Believing ambiguity causes error here