Peek Front Element of Queue in DSA C - Build from Scratch

Peek Front Element of Queue

📖 Scenario: Imagine a line of customers waiting at a ticket counter. We want to see who is at the front of the line without removing them.

🎯 Goal: You will create a queue of customer IDs, then write code to peek at the front customer without removing them.

📋 What You'll Learn

Create an integer array called queue with exactly these values: 101, 102, 103, 104, 105

Create an integer variable called front_index and set it to 0

Write code to peek the front element of the queue using queue[front_index]

Print the front element using printf with the exact format: "Front element: %d\n"

💡 Why This Matters

🌍 Real World

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

💼 Career

Understanding queues and how to peek at elements is important for software development, especially in areas like task scheduling and resource management.

1

Create the queue array

Create an integer array called queue with these exact values: 101, 102, 103, 104, 105

DSA C

# Your code here

Hint

Use curly braces to list the values inside the array.

2

Set the front index

Create an integer variable called front_index and set it to 0

DSA C

int queue[] = {101, 102, 103, 104, 105};
# Your code here

Hint

The front of the queue is at index 0 initially.

3

Peek the front element

Create an integer variable called front_element and set it to queue[front_index]

DSA C

int queue[] = {101, 102, 103, 104, 105};
int front_index = 0;
# Your code here

Hint

Use the front_index to get the front element from the queue array.

4

Print the front element

Print the front element using printf with the exact format: "Front element: %d\n" and the variable front_element

DSA C

int queue[] = {101, 102, 103, 104, 105};
int front_index = 0;
int front_element = queue[front_index];
# Your code here

Hint

Use printf to show the front element with the exact text and newline.

Practice

1. What does the peek operation do in a queue?

easy

A. Returns the front element without removing it

B. Removes the front element

C. Adds an element to the back

D. Checks if the queue is empty

Solution

1. Step 1: Understand the peek operation

   The peek operation looks at the front element of the queue without changing the queue.

2. Step 2: Compare with other operations

   Removing is done by dequeue, adding by enqueue, and checking empty is a separate check.

3. Final Answer:

   Returns the front element without removing it -> Option A

4. Quick Check:

   Peek = front element without removal [OK]

Hint: Peek shows front without removing [OK]

Common Mistakes:

• Confusing peek with dequeue
• Thinking peek adds elements
• Assuming peek checks emptiness

2. Which of the following is the correct C syntax to peek the front element of a queue named q implemented with an array and front index front?

easy

A. int x = q[front];

B. int x = q[rear];

C. int x = q[front + 1];

D. int x = q[0];

Solution

1. Step 1: Identify front element in array queue

   The front element is at index front in the array q.

2. Step 2: Check other options

   rear points to the back, front + 1 is next element, q[0] may not be front if front moved.

3. Final Answer:

   int x = q[front]; -> Option A

4. Quick Check:

   Peek front = q[front] [OK]

Hint: Peek uses front index, not rear or zero [OK]

Common Mistakes:

• Using rear index instead of front
• Adding 1 to front index incorrectly
• Assuming front is always zero

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

int q[5] = {10, 20, 30, 40, 50};
int front = 2;
printf("%d", q[front]);

medium

A. 10

B. 20

C. 30

D. 40

Solution

1. Step 1: Identify the element at index front

   Index 2 in array q is the third element, which is 30.

2. Step 2: Confirm output of printf

   Printing q[front] prints 30.

3. Final Answer:

   30 -> Option C

4. Quick Check:

   q[2] = 30 [OK]

Hint: Array index starts at 0, so q[2] is third element [OK]

Common Mistakes:

• Confusing index 2 with value 20
• Printing q[front + 1] by mistake
• Assuming front is zero

4. Identify the error in this C code snippet that tries to peek the front element of a queue:

int q[3] = {5, 10, 15};
int front = 3;
printf("%d", q[front]);

medium

A. Queue array is empty

B. front index is out of bounds

C. printf syntax error

D. No error, code is correct

Solution

1. Step 1: Check front index validity

   Array q has indices 0 to 2. front = 3 is outside bounds.

2. Step 2: Understand consequences

   Accessing q[3] causes undefined behavior or runtime error.

3. Final Answer:

   front index is out of bounds -> Option B

4. Quick Check:

   front must be within 0 to 2 [OK]

Hint: Front index must be inside array bounds [OK]

Common Mistakes:

• Ignoring array bounds
• Assuming front can be equal to array size
• Thinking printf syntax is wrong

5. Given a circular queue implemented with array q[5], front index front = 4, and rear index rear = 2, which expression correctly peeks the front element?

hard

A. q[front]

B. q[rear]

C. q[(rear + 1) % 5]

D. q[(front + 1) % 5]

Solution

1. Step 1: Understand circular queue front

   In a circular queue, the front element is at index (front + 1) % size, because front points to the last dequeued position.

2. Step 2: Check modulo usage

   Modulo is used to wrap around the array indices correctly.

3. Final Answer:

   q[(front + 1) % 5] -> Option D

4. Quick Check:

   Peek front = q[(front + 1) % size] in circular queue [OK]

Hint: In circular queue, front points behind the front element [OK]

Common Mistakes:

• Using q[front] directly in circular queue
• Confusing rear with front
• Assuming front is always zero