Base keyword behavior in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of base keyword in method override

What is the output of this C# program when calling obj.Show()?

C Sharp (C#)

class Parent {
    public virtual void Show() {
        System.Console.WriteLine("Parent Show");
    }
}
class Child : Parent {
    public override void Show() {
        System.Console.WriteLine("Child Show Start");
        base.Show();
        System.Console.WriteLine("Child Show End");
    }
}

var obj = new Child();
obj.Show();

A

Child Show Start
Parent Show
Child Show End

B

Parent Show
Child Show Start
Child Show End

C

Child Show Start
Child Show End
Parent Show

D

Child Show Start
Child Show Start
Child Show End

💡 Hint

Remember that base.Show() calls the parent class method inside the override.

The Child class overrides Show(). Inside it, it prints "Child Show Start", then calls base.Show() which runs the Parent version printing "Parent Show", then prints "Child Show End".

❓ Predict Output

intermediate

Using base constructor call

What will be printed when creating new Derived() with this code?

C Sharp (C#)

class Base {
    public Base() {
        System.Console.WriteLine("Base constructor");
    }
}
class Derived : Base {
    public Derived() : base() {
        System.Console.WriteLine("Derived constructor");
    }
}

var obj = new Derived();

A Derived constructor

B

Base constructor
Derived constructor

C

Derived constructor
Base constructor

D Base constructor

💡 Hint

The base constructor runs before the derived constructor body.

The Derived constructor explicitly calls base(), so the Base constructor runs first printing "Base constructor", then the Derived constructor prints "Derived constructor".

🔧 Debug

advanced

Why does this code cause a compile error?

This code tries to call base.Method() inside a static method. What error will the compiler show?

C Sharp (C#)

class A {
    public void Method() { }
}
class B : A {
    public static void StaticMethod() {
        base.Method();
    }
}

A Error: Keyword 'base' is not valid in a static context

B Error: Cannot call instance method from static method

C Error: Method does not exist in base class

D No error, code compiles fine

💡 Hint

The base keyword requires an instance context.

The base keyword can only be used inside instance methods because it refers to the current instance's base class. Static methods have no instance, so using base causes a compile error.

🧠 Conceptual

advanced

Effect of base keyword on property access

Given these classes, what will obj.Value print?

C Sharp (C#)

class Parent {
    public virtual int Value => 10;
}
class Child : Parent {
    public override int Value => base.Value + 5;
}

var obj = new Child();
System.Console.WriteLine(obj.Value);

A Compilation error

B 10

C 5

D 15

💡 Hint

The base keyword accesses the parent property value.

The Child overrides Value and returns base.Value + 5. Since base.Value is 10, the result is 15.

❓ Predict Output

expert

Using base keyword with indexers and virtual methods

What is the output of this program?

C Sharp (C#)

class Base {
    protected virtual string this[int index] => $"Base[{index}]";
    public virtual string GetValue(int i) => this[i];
}
class Derived : Base {
    protected override string this[int index] => $"Derived[{index}]";
    public override string GetValue(int i) {
        return base.GetValue(i) + ", " + this[i];
    }
}

var obj = new Derived();
System.Console.WriteLine(obj.GetValue(3));

A Base[3], Derived[3]

B Derived[3], Base[3]

C Derived[3], Derived[3]

D Base[3], Base[3]

💡 Hint

The base.GetValue(i) calls the base class method which uses the base indexer.

The base.GetValue(i) calls Base.GetValue which returns this[i]. Because this[i] is virtual and overridden, it calls Derived's indexer. So both calls use Derived's indexer. So the output is "Derived[3], Derived[3]".