﻿ 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];
int front = -1;
int back = -1;

// Function to insert an element into the queue
void enqueue(int item) {
if (back == MAX_SIZE - 1) {
printf("Error: Queue is full\n");
return;
}
if (front == -1) {
front = 0;
}
back++;
queue[back] = item;
}

// Function to display the elements in the queue
void display() {
if (front == -1 || front > back) {
printf("Queue is empty\n");
return;
}
printf("Queue elements are: ");
for (int i = front; i <= back; i++) {
printf("%d ", queue[i]);
}
printf("\n");
}

// Function to remove an element from a queue
void dequeue() {
if (front == -1 || front > back) {
printf("Error: Queue is empty\n");
return;
}
front++;
}

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

// Function to count the number of elements in a queue
int count() {
int count = 0;
if (front!=-1 && back!=-1)
{
for (int i = front; i <= back; i++) {
count++;
}
}
return count;
}

int main() {
printf("Initialize a queue!");
// Insert some elements into the queue.
printf("\nCheck the queue is empty or not? %s\n", is_empty() ? "Yes" : "No");
printf("Number of elements in queue: %d\n", count());
printf("\nInsert some elements into the queue:\n");
enqueue(1);
enqueue(2);
enqueue(3);
display();
// 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");
dequeue();
dequeue();
display();
printf("Number of elements in queue: %d\n", count());
printf("\nInsert another element into the queue:\n");
enqueue(4);
display();
printf("Number of elements in the queue: %d\n", count());
return 0;
}
```
```

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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﻿

## C Programming: Tips of the Day

C Programming - How do you pass a function as a parameter in C?

Declaration

A prototype for a function which takes a function parameter looks like the following:

```void func ( void (*f)(int) );
```

This states that the parameter f will be a pointer to a function which has a void return type and which takes a single int parameter. The following function (print) is an example of a function which could be passed to func as a parameter because it is the proper type:

```void print ( int x ) {
printf("%d\n", x);
}
```

Function Call

When calling a function with a function parameter, the value passed must be a pointer to a function. Use the function's name (without parentheses) for this:

```func(print);
```

would call func, passing the print function to it.

Function Body

As with any parameter, func can now use the parameter's name in the function body to access the value of the parameter. Let's say that func will apply the function it is passed to the numbers 0-4. Consider, first, what the loop would look like to call print directly:

```for ( int ctr = 0 ; ctr < 5 ; ctr++ ) {
print(ctr);
}
```

Since func's parameter declaration says that f is the name for a pointer to the desired function, we recall first that if f is a pointer then *f is the thing that f points to (i.e. the function print in this case). As a result, just replace every occurrence of print in the loop above with *f:

```void func ( void (*f)(int) ) {
for ( int ctr = 0 ; ctr < 5 ; ctr++ ) {
(*f)(ctr);
}
}
```

Ref : https://bit.ly/3skw9Um