Delegate declaration and instantiation in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of delegate invocation

What is the output of this C# code when the delegate is invoked?

C Sharp (C#)

delegate int Operation(int x, int y);

class Program {
    static int Add(int a, int b) => a + b;
    static void Main() {
        Operation op = Add;
        Console.WriteLine(op(3, 4));
    }
}

A 7

B 34

C 0

D Compilation error

💡 Hint

Remember that the delegate points to the Add method which sums two integers.

The delegate 'Operation' is assigned the method 'Add'. Calling op(3,4) invokes Add(3,4), which returns 7.

❓ Predict Output

intermediate

Delegate with anonymous method output

What will be printed when this C# program runs?

C Sharp (C#)

delegate string Formatter(string s);

class Program {
    static void Main() {
        Formatter f = delegate(string input) { return input.ToUpper(); };
        Console.WriteLine(f("hello"));
    }
}

A HELLO

B hello

C Hello

D Compilation error

💡 Hint

The anonymous method converts the string to uppercase.

The delegate 'Formatter' is assigned an anonymous method that returns the uppercase version of the input string. So 'hello' becomes 'HELLO'.

🔧 Debug

advanced

Identify the error in delegate instantiation

Which option correctly fixes the error in this delegate instantiation code?

C Sharp (C#)

delegate void Printer(string message);

class Program {
    static void PrintMessage() {
        Console.WriteLine("Hello World");
    }
    static void Main() {
        Printer p = PrintMessage;
        p("Test");
    }
}

A Change delegate return type to string: delegate string Printer(string message);

B Remove the parameter from delegate Printer: delegate void Printer();

C Call p() without arguments: p();

D Change PrintMessage to accept a string parameter: static void PrintMessage(string msg)

💡 Hint

The delegate expects a method with one string parameter, but PrintMessage has none.

The delegate 'Printer' requires a method that takes a string parameter. The method 'PrintMessage' has no parameters, so it must be changed to accept a string.

❓ Predict Output

advanced

Multicast delegate invocation output

What is the output of this C# program?

C Sharp (C#)

delegate void Notify();

class Program {
    static void Alert1() => Console.WriteLine("Alert 1");
    static void Alert2() => Console.WriteLine("Alert 2");
    static void Main() {
        Notify n = Alert1;
        n += Alert2;
        n();
    }
}

A Alert 2\nAlert 1

B Alert 1\nAlert 2

C Alert 1

D Compilation error

💡 Hint

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

The delegate 'n' calls Alert1 first, then Alert2, so both messages print in that order.

🧠 Conceptual

expert

Delegate instantiation with lambda expressions

Which option correctly declares and instantiates a delegate that takes two integers and returns their product using a lambda expression?

A Func multiply = (int x, int y) => x * y;

B delegate int multiply(int x, int y) => x * y;

C Func<int, int, int> multiply = (x, y) => x * y;

D var multiply = delegate(int x, int y) { return x + y; };

💡 Hint

Use Func<> for delegates with return values and lambda syntax for instantiation.

Option C correctly uses Func delegate type and a lambda expression returning the product. Option C is invalid syntax. Option C misses generic parameters. Option C returns sum, not product.