﻿ C - Number of elements in a queue

# C Exercises: Number of elements in a queue

## C Queue: Exercise-5 with Solution

Write a C program to count the number of elements in a queue.

Sample Solution:

C Code:

``````#include <stdio.h>
#define MAX_SIZE 100
int queue[MAX_SIZE]; // Declare an array to store elements of the queue
int front = -1; // Initialize front of the queue
int back = -1; // Initialize back of the queue

// 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) {
front = 0; // Set front to 0 if it's the first element being inserted
}
back++; // Increment the rear pointer
queue[back] = item; // Insert the item into the queue
}

// Function to display the elements in the queue
void display() {
if (front == -1 || front > back) { // Check if the queue is empty
printf("Queue is empty\n"); // Print message if the queue is empty
return;
}
printf("Queue elements are: "); // Print message to indicate displaying queue elements
for (int i = front; i <= back; i++) { // Loop through the queue elements
printf("%d ", queue[i]); // Print each element
}
printf("\n"); // Print a newline after displaying all elements
}

// Function to remove an element from the front of the queue
void 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;
}
front++; // Increment the front pointer to remove the element
}

// Function to check whether the queue is empty
int is_empty() {
if (front == -1 || front > back) { // Check if the queue is empty
return 1; // Return 1 if the queue is empty
}
return 0; // Otherwise, return 0
}

// Function to count the number of elements in the queue
int count() {
int count = 0; // Initialize count variable to store the number of elements
if (front != -1 && back != -1) { // Check if the queue is not empty
for (int i = front; i <= back; i++) { // Loop through the queue elements
count++; // Increment count for each element
}
}
return count; // Return the total count of elements in the queue
}

int main() {
printf("Initialize a queue!"); // Print message to indicate initializing a queue
// Insert some elements into the queue.
printf("\nCheck the queue is empty or not? %s\n", is_empty() ? "Yes" : "No"); // Check if the queue is empty
printf("Number of elements in queue: %d\n", count()); // Display the number of elements in the queue
printf("\nInsert some elements into the queue:\n"); // Print message to indicate inserting elements into the queue
enqueue(1); // Insert element 1 into the queue
enqueue(2); // Insert element 2 into the queue
enqueue(3); // Insert element 3 into the queue
display(); // Display the elements of the queue
// Display the number of elements in the queue
printf("Number of elements in queue: %d\n", count());
printf("\nDelete two elements from the said queue:\n"); // Print message to indicate deleting elements from the queue
dequeue(); // Delete one element from the queue
dequeue(); // Delete another element from the queue
display(); // Display the updated elements of the queue
printf("Number of elements in queue: %d\n", count()); // Display the updated number of elements in the queue
printf("\nInsert another element into the queue:\n"); // Print message to indicate inserting another element
enqueue(4); // Insert element 4 into the queue
display(); // Display the updated elements of the queue
printf("Number of elements in the queue: %d\n", count()); // Display the updated number of elements in the queue
return 0; // Return from the main function
}
```
```

Sample Output:

```Initialize a queue!
Check the queue is empty or not? Yes
Number of elements in queue: 0

Insert some elements into the queue:
Queue elements are: 1 2 3
Number of elements in queue: 3

Delete two elements from the said queue:
Queue elements are: 3
Number of elements in queue: 1

Insert another element into the queue:
Queue elements are: 3 4
Number of elements in the queue: 2
```

Flowchart:

C Programming Code Editor:

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