C Exercises: Delete the n^th element of a queue

Last update on March 19 2025 12:42:15 (UTC/GMT +8 hours)

11. Delete nth Element in Queue

Write a C program to delete the n^th element of a queue.

Firstly, this code checks if the queue is empty or if the position to delete is invalid. If the position is valid, it deletes the first n-1 elements, then deletes the nth element by calling the dequeue() function.

Sample Solution:

C Code:

#include <stdio.h>
#define MAX_SIZE 100

int queue[MAX_SIZE]; // Array to store elements of the queue
int front = -1, back = -1; // Initialize front and back pointers

// Function to insert an element into the queue
void enqueue(int item) {
    if (back == MAX_SIZE - 1) { // Check if the queue is full
        printf("Error: Queue is full\n"); // Print error message if the queue is full
        return;
    }
    if (front == -1) { // Check if the queue is empty
        front = 0; // If empty, set front to 0
    }
    back++; // Increment the back pointer
    queue[back] = item; // Add the item to the queue
}

// Function to remove an element from a queue
int dequeue() {
    if (front == -1 || front > back) { // Check if the queue is empty
        printf("Error: Queue is empty\n"); // Print error message if the queue is empty
        return -1; // Return -1 to indicate an empty queue
    }
    int item = queue[front]; // Get the front element of the queue
    front++; // Move the front pointer to the next element
    return item; // Return the removed element
}

// Function to delete the nth element of a queue
void delete_nth(int n) {
    if (front == -1 || front > back) { // Check if the queue is empty
        printf("Error: Queue is empty\n"); // Print error message if the queue is empty
        return;
    }
    if (n <= 0 || n > back - front + 1) { // Check if the position is valid
        printf("Error: Invalid position\n"); // Print error message if the position is invalid
        return;
    }

    // Delete the first n - 1 elements
    for (int i = 1; i < n; i++) {
        dequeue(); // Call dequeue to remove elements until reaching the nth position
    }

    // Delete the nth element
    dequeue(); // Call dequeue to remove the nth element
}

// Function to display the elements in the queue
void display_elements() {
    printf("Queue elements are: "); // Print message to indicate queue elements
    for (int i = front; i <= back; i++) { // Loop through the elements of the queue
        printf("%d ", queue[i]); // Print the current element
    }
    printf("\n"); // Print a newline after displaying all elements
}

int main() {
    // Insert some elements into the queue.
    printf("Insert some elements into the queue:\n");
    enqueue(1);
    enqueue(2);
    enqueue(3);
    enqueue(4);
    enqueue(5);
    display_elements(); // Display the elements in the queue
    // Delete the 7th element.
    printf("\nDelete the 7th element of the said queue:\n");
    delete_nth(7); // Attempt to delete the 7th element
    // Delete the 3rd element.
    printf("\nDelete the 3rd element of the said queue:\n");
    delete_nth(3); // Attempt to delete the 3rd element
    display_elements(); // Display the elements in the queue after deletion
    return 0; // Return 0 to indicate successful execution
}

Output:

Insert some elements into the queue:
Queue elements are: 1 2 3 4 5

Delete the 7th element of the said queue:
Error: Invalid position

Delete the 3rd element of the said queue:
Queue elements are: 4 5

Flowchart

For more Practice: Solve these Related Problems:

• Write a C program to implement a queue and delete the nth element from the front without shifting all subsequent elements.
• Write a C program to implement a circular queue where deletion of the nth element adjusts the front pointer correctly.
• Write a C program to implement a queue that deletes an element based on a condition rather than its fixed position.
• Write a C program to delete every kth element from a queue repeatedly until the queue is empty (Josephus problem style).

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