C# Collections MCQs

Question 21: What will be the output of the following code?

SortedList sortedList = new SortedList()
                            {
                                {2, true},
                                {1,"one"},
                            };
foreach(DictionaryEntry kvp in sortedList )
    Console.Write(kvp.Value);

Answer: D

Values can be of any data type in the SortedList. Learn C# SortedList.

Question 22: What will be the output of the following program? 

Stack myStack = new Stack(){
			1,2,3,4,5
		};
		
foreach (var itm in myStack)
	Console.Write(itm);

Answer: D

Stack does not support object initializer syntax. Use Push() method to add elements and Peek() or Pop() method to access it. Learn C# Stack.

Question 23: Which interface(s) must be implemented in the custom collection class in order to iterate it with the foreach loop?

Answer: B,C

Both IEnumerable and IEnumerator interfaces are required to be used with the foreach loop. IEnumerable interface contains the GetEnumerator() method, which returns an object of IEnumerator. IEnumerator interface contains MoveNext() and Reset() method which must be implement. Learn more about it here

Question 24: What will be the output of the following program?

public class Program
{
	public static void Main()
	{
		int[] arr = {1,2,3};
		Display(arr);
		
		ArrayList arList = new ArrayList(){ 4,5,6};
		Display(arList);
		
		IList lst = new List(){ 7,8,9};
		Display(lst);
	}
	
	public static void Display(IEnumerable col){
		foreach (var val in col)
			Console.Write(val); 
	}
}

Answer: D.

All the classes that implement the IEnumerable interface can be iterate using the foreach loop. Array, ArrayList, and IList implement IEnumerable interface, and so it can be iterate through a foreach loop.

Question 25: Which of the following collection stores key-value pairs?

Answer: D

SortedList, HashTable, and Dictionary stores key-value pairs.