C# OOP MCQs

Question 16: What will be the output of the following program?

class Printer
{
    public virtual void Install()
    {
        Console.WriteLine("Printer Installed.");
    }

    public virtual void Print(string text)
    {
        Console.WriteLine("Printing: " + text);
    }
}

class LaserPrinter : Printer
{
    public override void Install()
    {
        Console.WriteLine("Laser Printer Installed Successfully.");
    }
    public void InstallDrivers()
    {
        Console.WriteLine("Drivers for Laser Printer Installed.");
    }

}

Printer prnt = new LaserPrinter();
prnt.Install();

Answer: B

This is an example of run-time polymorphism, a.k.a. method overriding. The LaserPrinter class overrides the virtual method Install(), and so calling of the method is depends on the type of the object. Above, we created an object of the LaserPrinter, and so it will call the Install() method of the LaserPrinter class.

Question 17: What will be the output of the following program?

class Printer
{
    public virtual void Install()
    {
        Console.WriteLine("Printer Installed.");
    }

    public virtual void Print(string text)
    {
        Console.WriteLine("Printing: " + text);
    }
}

class LaserPrinter : Printer
{
    public void Install()
    {
        Console.WriteLine("Laser Printer Installed Successfully.");
    }
        
}

Printer printer1 = new LaserPrinter();
printer1.Install();

Answer: A

This is an example of method hiding. If a derived class defines an existing method of the base class without override the keyword, then the derived class method hides the base class method. The calling of the method depends on the type of a variable. C# compiler will give a warning for method hiding. Use the new keyword in the method declaration to remove the warning.