Enqueue Operation in DSA C# - Build from Scratch

Enqueue Operation

📖 Scenario: Imagine you are managing a line of customers waiting to buy tickets at a movie theater. Each new customer joins the end of the line. We will simulate this line using a queue data structure.

🎯 Goal: You will create a queue, add customers to it using the enqueue operation, and then display the queue to see the order of customers waiting.

📋 What You'll Learn

Create a queue of strings called ticketQueue.

Add three customers named exactly "Alice", "Bob", and "Charlie" to the queue using the enqueue operation.

Create a variable called newCustomer and set it to "Diana".

Add the newCustomer to the queue using the enqueue operation.

Print the contents of ticketQueue in order, separated by " -> ", ending with " -> null".

💡 Why This Matters

🌍 Real World

Queues are used in real life to manage lines, like customers waiting for service, print jobs waiting to print, or tasks waiting to be processed.

💼 Career

Understanding queues and the enqueue operation is important for software developers working on scheduling, task management, and real-time systems.

1

Create the initial queue

Create a queue of strings called ticketQueue and add these customers in order using Enqueue: "Alice", "Bob", "Charlie".

DSA C#

// Create the queue and add the first three customers
// Your code here

Hint

Use Queue<string> to create the queue and Enqueue to add customers.

2

Add a new customer variable

Create a string variable called newCustomer and set it to "Diana".

DSA C#

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        Queue ticketQueue = new Queue();
        ticketQueue.Enqueue("Alice");
        ticketQueue.Enqueue("Bob");
        ticketQueue.Enqueue("Charlie");

        // Create newCustomer variable
        // Your code here
    }
}

Hint

Use string newCustomer = "Diana"; to create the variable.

3

Enqueue the new customer

Add the newCustomer to the ticketQueue using the Enqueue method.

DSA C#

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        Queue ticketQueue = new Queue();
        ticketQueue.Enqueue("Alice");
        ticketQueue.Enqueue("Bob");
        ticketQueue.Enqueue("Charlie");

        string newCustomer = "Diana";

        // Add newCustomer to the queue
        // Your code here
    }
}

Hint

Use ticketQueue.Enqueue(newCustomer); to add the new customer.

4

Print the queue contents

Print the contents of ticketQueue in order, separated by " -> ", and end with " -> null". Use a foreach loop with variable customer to iterate over ticketQueue.

DSA C#

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        Queue ticketQueue = new Queue();
        ticketQueue.Enqueue("Alice");
        ticketQueue.Enqueue("Bob");
        ticketQueue.Enqueue("Charlie");

        string newCustomer = "Diana";

        ticketQueue.Enqueue(newCustomer);

        // Print the queue contents
        // Your code here
    }
}

Hint

Use a foreach loop to print each customer followed by " -> ", then print "null" at the end.

Practice

1. What does the Enqueue operation do in a queue data structure?

easy

A. Adds an element to the end of the queue

B. Removes an element from the front of the queue

C. Checks if the queue is empty

D. Returns the size of the queue

Solution

1. Step 1: Understand queue behavior

   A queue works like a line where new people join at the end.

2. Step 2: Define enqueue operation

   Enqueue means adding a new element at the back of the queue.

3. Final Answer:

   Adds an element to the end of the queue -> Option A

4. Quick Check:

   Enqueue = Add at end [OK]

Hint: Enqueue means add at the back of the queue [OK]

Common Mistakes:

• Confusing enqueue with dequeue
• Thinking enqueue removes elements
• Mixing enqueue with checking size

2. Which of the following is the correct syntax to enqueue an integer value 10 into a Queue<int> named q in C#?

easy

A. q.Enqueue(10);

B. q.Add(10);

C. q.Push(10);

D. q.Insert(10);

Solution

1. Step 1: Recall C# Queue method

   The method to add elements in Queue<T> is Enqueue.

2. Step 2: Match syntax

   Calling q.Enqueue(10); adds 10 to the queue correctly.

3. Final Answer:

   q.Enqueue(10); -> Option A

4. Quick Check:

   Use Enqueue() to add in C# Queue [OK]

Hint: Use Enqueue() method to add elements in C# Queue [OK]

Common Mistakes:

• Using Add() which is not in Queue
• Using Push() which is for stacks
• Using Insert() which is not a Queue method

3. What will be the output of the following C# code?

Queue<string> q = new Queue<string>();
q.Enqueue("apple");
q.Enqueue("banana");
q.Enqueue("cherry");
Console.WriteLine(string.Join(", ", q));

medium

A. cherry, banana, apple

B. apple, banana, cherry

C. banana, cherry, apple

D. apple, cherry, banana

Solution

1. Step 1: Trace enqueue order

   Elements are added in order: apple, then banana, then cherry.

2. Step 2: Understand queue order

   Queue keeps order of insertion, so printing shows apple, banana, cherry.

3. Final Answer:

   apple, banana, cherry -> Option B

4. Quick Check:

   Queue prints in enqueue order [OK]

Hint: Queue keeps insertion order; output matches enqueue sequence [OK]

Common Mistakes:

• Assuming reverse order output
• Mixing enqueue with stack behavior
• Confusing output order with dequeue

4. Identify the error in the following code snippet that tries to enqueue an element into a queue:

Queue<int> q = new Queue<int>();
q.Enqueue(5);
q.Enqueue(10);
q.Enqueue(15);
q.Enqueue();

medium

A. Cannot enqueue integer values

B. Queue is not initialized

C. Enqueue method does not exist

D. Missing argument in the last Enqueue call

Solution

1. Step 1: Check method calls

   The last call q.Enqueue(); has no argument, but Enqueue requires one.

2. Step 2: Confirm method signature

   Enqueue needs a value to add, so missing argument causes error.

3. Final Answer:

   Missing argument in the last Enqueue call -> Option D

4. Quick Check:

   Enqueue requires one argument [OK]

Hint: Enqueue always needs one argument to add [OK]

Common Mistakes:

• Calling Enqueue without argument
• Assuming Enqueue can be empty
• Confusing initialization errors

5. You have a queue q with elements [1, 2, 3]. You want to enqueue elements 4 and 5, but only if the queue size is less than 5. Which code snippet correctly performs this conditional enqueue operation in C#?

hard

A. if (q.Count == 5) { q.Enqueue(4); q.Enqueue(5); }

B. if (q.Count <= 5) { q.Enqueue(4); q.Enqueue(5); }

C. if (q.Count < 5) { q.Enqueue(4); q.Enqueue(5); }

D. if (q.Count > 5) { q.Enqueue(4); q.Enqueue(5); }

Solution

1. Step 1: Understand queue size condition

   We want to add only if size is less than 5, so condition is q.Count < 5.

2. Step 2: Apply enqueue calls inside condition

   If condition is true, enqueue 4 and 5 to add them safely.

3. Final Answer:

   if (q.Count < 5) { q.Enqueue(4); q.Enqueue(5); } -> Option C

4. Quick Check:

   Use < 5 to check size before enqueue [OK]

Hint: Check queue size with Count before enqueueing [OK]

Common Mistakes:

• Using <= instead of < causing overflow
• Using > or == which are wrong conditions
• Not checking size before enqueue