Optional parameters in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a method with an optional parameter.

C Sharp (C#)

void Greet(string name, string greeting = [1]) {
    Console.WriteLine($"{greeting}, {name}!");
}

Drag options to blanks, or click blank then click option'

A"Hey"

B"Welcome"

C"Hi"

D"Hello"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to assign a default value to the optional parameter.

Using a variable instead of a constant as the default value.

The optional parameter greeting is given a default value "Hello". This means if no argument is passed for greeting, it uses "Hello".

2fill in blank

medium

Complete the code to call the method using the optional parameter.

C Sharp (C#)

Greet("Alice", [1]);

Drag options to blanks, or click blank then click option'

A"Good morning"

BGood morning

CHello

Dgreeting

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a string without quotes.

Passing the parameter name instead of a value.

When calling the method, the optional parameter can be passed as a string literal in quotes.

3fill in blank

hard

Fix the error in the method declaration with an optional parameter.

C Sharp (C#)

void Display(int count, string message [1]) {
    Console.WriteLine($"{message}: {count}");
}

Drag options to blanks, or click blank then click option'

A== "Default"

B: "Default"

C= "Default"

D=> "Default"

Attempts:

3 left

💡 Hint

Common Mistakes

Using : or => instead of = for default values.

Omitting the default value assignment.

Optional parameters require an equals sign (=) followed by the default value.

4fill in blank

hard

Fill both blanks to declare a method with two optional parameters.

C Sharp (C#)

void ShowInfo(string name, int age = [1], string city = [2]) {
    Console.WriteLine($"{name}, {age}, {city}");
}

Drag options to blanks, or click blank then click option'

A30

Bnull

C"Unknown"

D"None"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around integer default values.

Not using quotes around string default values.

The optional parameters age and city have default values 30 and "Unknown" respectively.

5fill in blank

hard

Fill all three blanks to call the method using named and optional parameters.

C Sharp (C#)

ShowInfo(name: [1], city: [2], age: [3]);

Drag options to blanks, or click blank then click option'

A"Bob"

B"Paris"

C25

D"Alice"

Attempts:

3 left

💡 Hint

Common Mistakes

Using unnamed arguments in the wrong order.

Forgetting quotes around string arguments.

The method is called with named arguments: name="Alice", city="Paris", age=25.

Practice

1. What is the main purpose of optional parameters in C# methods?

easy

A. To force all arguments to be passed every time

B. To make methods run faster

C. To allow skipping some arguments by providing default values

D. To declare variables inside methods

Solution

1. Step 1: Understand optional parameters

   Optional parameters let you give default values so callers can skip them.

2. Step 2: Compare with other options

   Options A, C, and D do not describe optional parameters correctly.

3. Final Answer:

   To allow skipping some arguments by providing default values -> Option C

4. Quick Check:

   Optional parameters = skip arguments with defaults [OK]

Hint: Optional parameters have default values to skip arguments [OK]

Common Mistakes:

• Thinking optional parameters speed up code
• Believing all arguments must always be passed
• Confusing optional parameters with local variables

2. Which of the following method signatures correctly uses optional parameters in C#?

easy

A. void Print(string message, int count = 1)

B. void Print(int count, string message)

C. void Print(int count = 1, string message)

D. void Print(string message = "Hello", int count)

Solution

1. Step 1: Recall optional parameter rules

   Optional parameters must come after all required parameters.

2. Step 2: Check each signature

   A: optional first - invalid. B: no default value, so no optional parameter. C: optional first - invalid. D: optional last - correct.

3. Final Answer:

   void Print(string message, int count = 1) -> Option A

4. Quick Check:

   Optional parameters come last = D [OK]

Hint: Optional parameters must be last in method signature [OK]

Common Mistakes:

• Placing optional parameters before required ones
• Missing default values for optional parameters
• Confusing parameter order rules

3. What is the output of this C# code?

void Greet(string name = "Guest", int times = 1) {
  for (int i = 0; i < times; i++) {
    Console.WriteLine($"Hello, {name}!");
  }
}

Greet("Alice");

medium

A. Hello, Guest! printed multiple times

B. Hello, Guest! printed once

C. Hello, Alice! printed zero times

D. Hello, Alice! printed once

Solution

1. Step 1: Analyze method call

   Greet is called with "Alice" only, so name = "Alice", times uses default 1.

2. Step 2: Understand loop behavior

   The loop runs once (times = 1), printing "Hello, Alice!" once.

3. Final Answer:

   Hello, Alice! printed once -> Option D

4. Quick Check:

   Passed name, default times = 1 [OK]

Hint: Passed args override defaults; missing ones use default [OK]

Common Mistakes:

• Assuming default name is used when argument is passed
• Thinking loop runs zero or multiple times incorrectly
• Confusing parameter order and values

4. Identify the error in this method declaration:

public void Display(int x = 5, int y) {
  Console.WriteLine(x + y);
}

medium

A. Missing return type

B. Optional parameter must come after all required parameters

C. Cannot use Console.WriteLine inside methods

D. Parameters must have different names

Solution

1. Step 1: Check parameter order

   Parameter x is optional but comes before required parameter y, which is invalid.

2. Step 2: Verify other options

   Return type is present (void), Console.WriteLine is valid, parameter names are unique.

3. Final Answer:

   Optional parameter must come after all required parameters -> Option B

4. Quick Check:

   Optional params last rule violated [OK]

Hint: Optional parameters must be last in parameter list [OK]

Common Mistakes:

• Placing optional parameters before required ones
• Thinking Console.WriteLine is invalid in methods
• Confusing parameter naming rules

5. You want to create a method CalculateTotal that adds two numbers but allows skipping the second number, which defaults to 10. Which method signature is correct and how would you call it to add 5 and the default 10?

hard

A. public int CalculateTotal(int a, int b = 10) { return a + b; } Call: CalculateTotal(5);

B. public int CalculateTotal(int a = 10, int b) { return a + b; } Call: CalculateTotal(5);

C. public int CalculateTotal(int a, int b) { return a + b; } Call: CalculateTotal(5);

D. public int CalculateTotal(int a = 10, int b = 5) { return a + b; } Call: CalculateTotal();

Solution

1. Step 1: Check method signature rules

   Optional parameter b must come after required a, with default 10.

2. Step 2: Check method call

   Calling CalculateTotal(5) passes a=5, b uses default 10, sum is 15.

3. Final Answer:

   public int CalculateTotal(int a, int b = 10) { return a + b; } Call: CalculateTotal(5); -> Option A

4. Quick Check:

   Optional param last, call with one arg uses default [OK]

Hint: Put optional params last and call with fewer args to use defaults [OK]

Common Mistakes:

• Placing optional parameter before required one
• Calling method without required arguments
• Assuming default values apply when arguments are passed