Params keyword for variable arguments in C Sharp (C#) - Mini Project: Build & Apply

Using the Params Keyword for Variable Arguments

📖 Scenario: Imagine you are creating a simple calculator that can add any number of integers given by the user. Instead of writing many methods for different numbers of inputs, you want one method that can take any amount of numbers.

🎯 Goal: Build a C# program that uses the params keyword to create a method which adds any number of integers and returns the total sum.

📋 What You'll Learn

Create a method called AddNumbers that uses the params keyword to accept multiple integers.

Call the AddNumbers method with different numbers of arguments.

Print the sum returned by the AddNumbers method.

💡 Why This Matters

🌍 Real World

Using the <code>params</code> keyword helps create flexible methods that can handle different amounts of input without writing many overloads.

💼 Career

Many programming jobs require writing clean, reusable code. Knowing how to use <code>params</code> helps you write methods that are easy to use and maintain.

1

Create the AddNumbers method with params

Write a method called AddNumbers that takes a params int[] numbers parameter and returns an int. Inside the method, create a variable sum initialized to 0.

C Sharp (C#)

// Your code here

Hint

Use params int[] numbers in the method parameter to accept any number of integers.

2

Add numbers inside the AddNumbers method

Inside the AddNumbers method, use a foreach loop with variable num to iterate over numbers and add each num to sum. Then return sum.

C Sharp (C#)

using System;

class Program
{
    static int AddNumbers(params int[] numbers)
    {
        int sum = 0;
        // Use foreach loop to add numbers
        // Your code here
    }

    static void Main()
    {
    }
}

Hint

Use foreach (int num in numbers) to loop through all numbers.

3

Call AddNumbers with different argument counts

In the Main method, call AddNumbers with these arguments: 1, 2, 3 and store the result in result1. Then call AddNumbers with 4, 5, 6, 7, 8 and store the result in result2.

C Sharp (C#)

using System;

class Program
{
    static int AddNumbers(params int[] numbers)
    {
        int sum = 0;
        foreach (int num in numbers)
        {
            sum += num;
        }
        return sum;
    }

    static void Main()
    {
        // Call AddNumbers with 1, 2, 3 and store in result1
        // Call AddNumbers with 4, 5, 6, 7, 8 and store in result2
        // Your code here
    }
}

Hint

Call AddNumbers with the exact numbers and store results in result1 and result2.

4

Print the results

In the Main method, print result1 and result2 each on a new line using Console.WriteLine.

C Sharp (C#)

using System;

class Program
{
    static int AddNumbers(params int[] numbers)
    {
        int sum = 0;
        foreach (int num in numbers)
        {
            sum += num;
        }
        return sum;
    }

    static void Main()
    {
        int result1 = AddNumbers(1, 2, 3);
        int result2 = AddNumbers(4, 5, 6, 7, 8);
        // Print result1 and result2
        // Your code here
    }
}

Hint

Use Console.WriteLine(result1); and Console.WriteLine(result2); to print the sums.

Practice

1. What does the params keyword do in a C# method?

easy

A. Makes the method run faster by optimizing loops.

B. Allows the method to accept a variable number of arguments as an array.

C. Declares a method as asynchronous.

D. Specifies that the method returns multiple values.

Solution

1. Step 1: Understand the purpose of params

   The params keyword allows a method to accept zero or more arguments as a single array parameter.

2. Step 2: Compare with other options

   Options B, C, and D describe unrelated features: performance, async methods, and multiple return values, which params does not do.

3. Final Answer:

   Allows the method to accept a variable number of arguments as an array. -> Option B

4. Quick Check:

   params = variable arguments [OK]

Hint: Remember: params means flexible number of inputs [OK]

Common Mistakes:

• Thinking params changes method speed
• Confusing params with async keyword
• Believing params allows multiple return values

2. Which of the following is the correct syntax to declare a method using params in C#?

easy

A. public void PrintNumbers(params int numbers[]) { }

B. public void PrintNumbers(int params[] numbers) { }

C. public void PrintNumbers(int[] params numbers) { }

D. public void PrintNumbers(params int[] numbers) { }

Solution

1. Step 1: Recall correct params syntax

   The params keyword comes before the array type and parameter name: params int[] numbers.

2. Step 2: Identify incorrect placements

   Options B, C, and D place params incorrectly or use invalid syntax for arrays in C#.

3. Final Answer:

   public void PrintNumbers(params int[] numbers) { } -> Option D

4. Quick Check:

   params before array type [OK]

Hint: Put params right before the array type [OK]

Common Mistakes:

• Placing params after the type or variable name
• Using square brackets incorrectly
• Confusing params with pointer syntax

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

public class Program {
  public static void PrintAll(params string[] words) {
    foreach (var word in words) {
      Console.Write(word + " ");
    }
  }
  public static void Main() {
    PrintAll("hello", "world", "!");
  }
}

medium

A. hello world !

B. hello world!

C. hello, world, !

D. Compilation error

Solution

1. Step 1: Understand method call with params

   The method PrintAll accepts any number of strings as an array and prints each with a space after it.

2. Step 2: Trace the output

   It prints "hello ", then "world ", then "! ", resulting in "hello world ! " with spaces after each word.

3. Final Answer:

   hello world ! -> Option A

4. Quick Check:

   Params prints each argument with space [OK]

Hint: Params passes arguments as array, loop prints each [OK]

Common Mistakes:

• Missing spaces between words
• Expecting commas instead of spaces
• Thinking it causes compile errors

4. Identify the error in this method declaration:

public void Show(params int[] numbers, string label) {
  Console.WriteLine(label);
}

medium

A. The 'params' parameter must be the last parameter in the method.

B. The 'params' keyword cannot be used with arrays.

C. The method must return a value when using 'params'.

D. The 'params' keyword requires the parameter to be optional.

Solution

1. Step 1: Check parameter order rules for params

   The params parameter must be the last one in the method signature.

2. Step 2: Identify the error

   Here, params int[] numbers is before string label, which is invalid.

3. Final Answer:

   The 'params' parameter must be the last parameter in the method. -> Option A

4. Quick Check:

   params must be last [OK]

Hint: Params must always be last parameter [OK]

Common Mistakes:

• Placing params before other parameters
• Thinking params can be anywhere
• Confusing params with optional parameters

5. You want to create a method SumAll that sums any number of integers passed to it. Which of these method declarations correctly uses params and returns the sum?

hard

A. public int SumAll(params int numbers) { return numbers.Length; }

B. public int SumAll(int[] numbers, params int n) { return numbers.Sum() + n; }

C. public int SumAll(params int[] numbers) { int sum = 0; foreach(var n in numbers) sum += n; return sum; }

D. public int SumAll(params int[] numbers) { return numbers[0]; }

Solution

1. Step 1: Check correct use of params and summing logic

   public int SumAll(params int[] numbers) { int sum = 0; foreach(var n in numbers) sum += n; return sum; } correctly declares params int[] numbers and sums all elements in a loop.

2. Step 2: Evaluate other options

   public int SumAll(int[] numbers, params int n) { return numbers.Sum() + n; } has invalid params int n after array; public int SumAll(params int numbers) { return numbers.Length; } uses params int numbers which is invalid; public int SumAll(params int[] numbers) { return numbers[0]; } returns only first element, not sum.

3. Final Answer:

   public int SumAll(params int[] numbers) { int sum = 0; foreach(var n in numbers) sum += n; return sum; } -> Option C

4. Quick Check:

   Params array summed with loop [OK]

Hint: Params must be array; sum with loop or LINQ [OK]

Common Mistakes:

• Using params with single int instead of array
• Placing params parameter incorrectly
• Returning only first element instead of sum