Why delegates are needed in C Sharp (C#) - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of delegate invocation

What is the output of this C# code that uses a delegate to call a method?

C Sharp (C#)

using System;

public delegate void Notify(string message);

class Program {
    static void Main() {
        Notify notify = ShowMessage;
        notify("Hello, delegate!");
    }

    static void ShowMessage(string msg) {
        Console.WriteLine(msg);
    }
}

A Hello, delegate!

B ShowMessage

C Compile-time error

D Runtime exception

💡 Hint

Look at how the delegate calls the method ShowMessage with a string argument.

The delegate 'Notify' points to the method 'ShowMessage'. When invoked with a string, it calls ShowMessage which prints the message.

🧠 Conceptual

intermediate

Why use delegates in C#?

Which of these best explains why delegates are needed in C#?

A To create variables that hold numbers only.

B To replace all classes with functions.

C To store data in a list.

D To allow methods to be passed as parameters and enable flexible callback mechanisms.

💡 Hint

Think about how you might want to call different methods dynamically.

Delegates let you treat methods like variables, so you can pass them around and call them later, enabling callbacks and event handling.

❓ Predict Output

advanced

Multicast delegate output

What will be the output of this C# program using a multicast delegate?

C Sharp (C#)

using System;

public delegate void Notify();

class Program {
    static void Main() {
        Notify notify = First;
        notify += Second;
        notify();
    }

    static void First() {
        Console.WriteLine("First called");
    }

    static void Second() {
        Console.WriteLine("Second called");
    }
}

A First called\nSecond called

B Compile-time error

C First called

D Second called\nFirst called

💡 Hint

Multicast delegates call all methods in the order they were added.

The delegate 'notify' calls First then Second because both methods are added to the invocation list.

❓ Predict Output

advanced

Delegate with return value behavior

What is the output of this C# code where a delegate has multiple methods with return values?

C Sharp (C#)

using System;

public delegate int Calculate(int x, int y);

class Program {
    static void Main() {
        Calculate calc = Add;
        calc += Multiply;
        int result = calc(3, 4);
        Console.WriteLine(result);
    }

    static int Add(int a, int b) {
        return a + b;
    }

    static int Multiply(int a, int b) {
        return a * b;
    }
}

A 7\n12

B 7

C 12

D Compile-time error

💡 Hint

When a multicast delegate returns a value, only the last method's return is used.

The delegate calls Add then Multiply, but only Multiply's return value (3*4=12) is stored in result.

🧠 Conceptual

expert

Delegate use in event handling

Why are delegates essential for event handling in C#?

A Because they replace the need for classes in event-driven programs.

B Because they allow methods to be assigned and called dynamically when events occur.

C Because they store event data in variables.

D Because they automatically generate user interface elements.

💡 Hint

Think about how events notify multiple methods when something happens.

Delegates let events keep a list of methods to call when triggered, enabling dynamic and flexible event responses.