Params keyword for variable arguments in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method using params keyword

What is the output of this C# program?

C Sharp (C#)

using System;
class Program {
    static void PrintNumbers(params int[] numbers) {
        foreach (var num in numbers) {
            Console.Write(num + " ");
        }
    }
    static void Main() {
        PrintNumbers(1, 2, 3);
    }
}

A System.Int32[]

B 1, 2, 3

C 1 2 3

D Error: params keyword not allowed

💡 Hint

Remember, params allows passing multiple arguments as an array.

The method PrintNumbers accepts any number of integers using params. It prints each number followed by a space, so the output is 1 2 3 .

❓ Predict Output

intermediate

Output when passing an array to a params parameter

What will this program print?

C Sharp (C#)

using System;
class Program {
    static void ShowItems(params string[] items) {
        foreach (var item in items) {
            Console.Write(item + ",");
        }
    }
    static void Main() {
        string[] fruits = {"apple", "banana"};
        ShowItems(fruits);
    }
}

A System.String[],

B apple,banana,

C apple, banana,

D Error: Cannot convert string[] to params string[]

💡 Hint

Passing an array to a params parameter passes all elements as arguments.

The array fruits is passed to ShowItems which treats it as multiple arguments. It prints each fruit followed by a comma, resulting in apple,banana,.

❓ Predict Output

advanced

Output when mixing normal and params parameters

What is the output of this program?

C Sharp (C#)

using System;
class Program {
    static void Display(string title, params int[] numbers) {
        Console.Write(title + ": ");
        foreach (var n in numbers) {
            Console.Write(n + " ");
        }
    }
    static void Main() {
        Display("Numbers", 5, 10, 15);
    }
}

A Numbers: 5 10 15

B Numbers: 5,10,15

C Numbers: System.Int32[]

D Error: params must be last parameter

💡 Hint

The params parameter must be last and collects all extra arguments.

The method prints the title then all numbers separated by spaces. The output is Numbers: 5 10 15 .

❓ Predict Output

advanced

What error occurs with params not last?

What error will this code produce?

C Sharp (C#)

class Program {
    static void Test(params int[] numbers, string label) {
    }
}

A Compile-time error: missing return type

B Runtime error: invalid params usage

C No error, compiles fine

D Compile-time error: params must be last parameter

💡 Hint

Check the position of the params parameter.

The params parameter must be the last in the method signature. Here it is not last, so the compiler gives an error.

🧠 Conceptual

expert

How many items in params array when called with no arguments?

Consider this method:

void PrintAll(params string[] items) { Console.WriteLine(items.Length); }

What will be printed when calling PrintAll() with no arguments?

A 0

B 1

C null

D Compile-time error

💡 Hint

Think about what params does when no arguments are passed.

When no arguments are passed, the params array is an empty array, so items.Length is 0.