Constructor overloading in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of overloaded constructors with default values

What is the output of this C# program using constructor overloading?

C Sharp (C#)

using System;
class Box {
    public int length, width, height;
    public Box() {
        length = 1; width = 1; height = 1;
    }
    public Box(int l, int w, int h) {
        length = l; width = w; height = h;
    }
    public void Display() {
        Console.WriteLine($"{length} {width} {height}");
    }
}
class Program {
    static void Main() {
        Box b1 = new Box();
        Box b2 = new Box(2, 3, 4);
        b1.Display();
        b2.Display();
    }
}

A 1 1 1\n2 3 4

B 0 0 0\n2 3 4

C 1 1 1\n0 0 0

D 2 3 4\n1 1 1

💡 Hint

Look at which constructor is called for each object.

The first Box uses the parameterless constructor setting all dimensions to 1. The second Box uses the constructor with parameters, setting length=2, width=3, height=4.

❓ Predict Output

intermediate

Which constructor is called?

Given this class with overloaded constructors, what will be printed when creating new Person("Alice")?

C Sharp (C#)

using System;
class Person {
    public string name;
    public int age;
    public Person() {
        name = "Unknown";
        age = 0;
    }
    public Person(string n) {
        name = n;
        age = 18;
    }
    public Person(string n, int a) {
        name = n;
        age = a;
    }
    public void Display() {
        Console.WriteLine($"Name: {name}, Age: {age}");
    }
}
class Program {
    static void Main() {
        Person p = new Person("Alice");
        p.Display();
    }
}

A Name: Unknown, Age: 0

B Name: Alice, Age: 0

C Name: Unknown, Age: 18

D Name: Alice, Age: 18

💡 Hint

Check which constructor matches the argument list.

The constructor with one string parameter sets name to the argument and age to 18.

❓ Predict Output

advanced

Output with constructor chaining

What is the output of this program that uses constructor chaining in C#?

C Sharp (C#)

using System;
class Car {
    public string brand;
    public string model;
    public int year;

    public Car() : this("Unknown", "Unknown", 0) {}
    public Car(string brand) : this(brand, "Unknown", 0) {}
    public Car(string brand, string model) : this(brand, model, 2020) {}
    public Car(string brand, string model, int year) {
        this.brand = brand;
        this.model = model;
        this.year = year;
    }
    public void Display() {
        Console.WriteLine($"{brand} {model} {year}");
    }
}
class Program {
    static void Main() {
        Car c1 = new Car();
        Car c2 = new Car("Toyota");
        Car c3 = new Car("Honda", "Civic");
        Car c4 = new Car("Ford", "Mustang", 1969);
        c1.Display();
        c2.Display();
        c3.Display();
        c4.Display();
    }
}

A Unknown Unknown 0\nToyota Unknown 2020\nHonda Civic 2020\nFord Mustang 1969

B Unknown Unknown 0\nToyota Unknown 0\nHonda Civic 0\nFord Mustang 1969

C Unknown Unknown 0\nToyota Unknown 0\nHonda Civic 2020\nFord Mustang 1969

D Unknown Unknown 2020\nToyota Unknown 0\nHonda Civic 2020\nFord Mustang 1969

💡 Hint

Follow the constructor calls from the parameterless to the full constructor.

Each constructor calls the next with default values. The year defaults to 0 except for the two-parameter constructor which sets year to 2020.

❓ Predict Output

advanced

What error occurs with this constructor call?

What error will this code produce when trying to create new Employee(123, "John")?

C Sharp (C#)

using System;
class Employee {
    public int id;
    public string name;
    public Employee(string name) {
        this.name = name;
        id = 0;
    }
    public Employee(int id) {
        this.id = id;
        name = "Unknown";
    }
}
class Program {
    static void Main() {
        Employee e = new Employee(123, "John");
        Console.WriteLine($"ID: {e.id}, Name: {e.name}");
    }
}

A Compile-time error: no constructor takes 2 arguments

B Runtime error: NullReferenceException

C Output: ID: 123, Name: John

D Output: ID: 0, Name: Unknown

💡 Hint

Check the constructors defined and the arguments passed.

No constructor matches two parameters (int, string), so compiler error occurs.

🧠 Conceptual

expert

How many constructors are called in this chain?

Consider this class with constructor overloading and chaining. How many constructors are called when creating new Gadget()?

C Sharp (C#)

class Gadget {
    public Gadget() : this(10) {}
    public Gadget(int size) : this(size, "Standard") {}
    public Gadget(int size, string type) {
        // Initialization code
    }
}

A 1

B 3

C 2

D 0

💡 Hint

Count each constructor call in the chain starting from the parameterless one.

The parameterless constructor calls the one with int, which calls the one with int and string, so 3 constructors are called in total.