C# OOP MCQs

Question 11: What will be the output of the following program?

class Person
{
    public void Introduction(){ 
        Console.WriteLine("I am a person.");
    }

    public string Introduction(){ 
        return "I am a person.";
    }
}

Answer: C

This is an example of method overloading, but it will give a compile-time error because two methods are defined with the same name and same parameters. They should either have different numbers or types or sequences of parameters for valid method overloading. Return types are not considered in the method overloading.

Question 12: What will be the output of the following program?

class Person
{
    public void Introduction(){ 
        Console.WriteLine("I am a person.");
    }

    public void Introduction(string name){ 
        Console.WriteLine("My name is " + name);
    }
        
    public void Introduction(string name, int age = 0){ 
        Console.WriteLine($"My name is {name} and age is {age}");
    }
}

Person p = new Person();
p.Introduction("Steve");

Answer: A

This will call the Introduction() method, which has one parameter, since Introduction() method is called with one parameter.

Question 13: What will be the output of the following program?

class Person
{
    public void Introduction(int age, string name){ 
        Console.WriteLine("My name is " + name);
    }
        
    public void Introduction(string name, int age=0){ 
        Console.WriteLine($"My name is {name} and age is {age}");
    }
       
}

Person p = new Person();
p.Introduction("Steve");

Answer: B

This will execute the second Introduction() method as it includes the first string parameter and the int parameter is optional with the default value.

Question 14: What will be the output of the following program?

class Person
{
    public void Introduction(int age = 0, string name){ 
        Console.WriteLine("My name is " + name);
    }
        
    public void Introduction(string name, int age=0){ 
        Console.WriteLine($"My name is {name} and age is {age}");
    }
}

Person p = new Person();
p.Introduction("Steve");

Answer: C

This will give a compile-time error because the first Introduction() method includes the first parameter as an optional parameter. An optional parameter must come last.

Question 15: What will be the output of the following program?

class Shape
{
    public int Sides { get; set; }
}

class Square : Shape
{
        
}

class Program
{
    public static void Display(Square s){
        Console.WriteLine($"Sides: {s.Sides}");
    }

    public static void Main()
    {
        Shape sq = new Square();
        Sq.Sides = 4;
        Display(sq); 
    }  
}

Answer: D

The Display() method takes a parameter of the Square type, but we pass a variable of Shape type. C# cannot convert base type to derived type implicitly. We must explicitly cast it to the Square type before passing it to the Display() method. The above example will give compile-time error “Argument 1: cannot convert from 'Shape' to 'Square'”

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.