C Program to Implement Priority Queue Operations

This is a C Program to implement priority queue to add and delete elements.

Problem Description

This C program implements the operations of the priority queue.

Problem Solution

1. Add the elements into the queue according to the order (ascending or descending).
2. Delete the elements.

Program/Source Code

Here is source code of the C Program to implement priority queue to add and delete elements. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/* 
```

 * C Program to Implement Priority Queue to Add and Delete Elements

```
 */
```
```
#include <stdio.h>
```
```
#include <stdlib.h>
```
```
 
```
```
#define MAX 5
```
```
 
```
```
void insert_by_priority(int);
```
```
void delete_by_priority(int);
```
```
void create();
```
```
void check(int);
```
```
void display_pqueue();
```
```
 
```
```
int pri_que[MAX];
```
```
int front, rear;
```
```
 
```
```
void main()
```
```
{
```
```
    int n, ch;
```
```
 
```

    printf("\n1 - Insert an element into queue");

    printf("\n2 - Delete an element from queue");

    printf("\n3 - Display queue elements");

```
    printf("\n4 - Exit");
```
```
 
```
```
    create();
```
```
 
```
```
    while (1)
```
```
    {
```

        printf("\nEnter your choice : ");

```
        scanf("%d", &ch);
```
```
 
```
```
        switch (ch)
```
```
        {
```
```
        case 1: 
```

            printf("\nEnter value to be inserted : ");

```
            scanf("%d",&n);
```
```
            insert_by_priority(n);
```
```
            break;
```
```
        case 2:
```

            printf("\nEnter value to delete : ");

```
            scanf("%d",&n);
```
```
            delete_by_priority(n);
```
```
            break;
```
```
        case 3: 
```
```
            display_pqueue();
```
```
            break;
```
```
        case 4: 
```
```
            exit(0);
```
```
        default: 
```

            printf("\nChoice is incorrect, Enter a correct choice");

```
        }
```
```
    }
```
```
}
```
```
 
```

/* Function to create an empty priority queue */

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void create()
```
```
{
```
```
    front = rear = -1;
```
```
}
```
```
 
```

/* Function to insert value into priority queue */

```
void insert_by_priority(int data)
```
```
{
```
```
    if (rear >= MAX - 1)
```
```
    {
```

        printf("\nQueue overflow no more elements can be inserted");

```
        return;
```
```
    }
```
```
    if ((front == -1) && (rear == -1))
```
```
    {
```
```
        front++;
```
```
        rear++;
```
```
        pri_que[rear] = data;
```
```
        return;
```
```
    }    
```
```
    else
```
```
        check(data);
```
```
    rear++;
```
```
}
```
```
 
```

/* Function to check priority and place element */

```
void check(int data)
```
```
{
```
```
    int i,j;
```
```
 
```
```
    for (i = 0; i <= rear; i++)
```
```
    {
```
```
        if (data >= pri_que[i])
```
```
        {
```

            for (j = rear + 1; j > i; j--)

```
            {
```

                pri_que[j] = pri_que[j - 1];

```
            }
```
```
            pri_que[i] = data;
```
```
            return;
```
```
        }
```
```
    }
```
```
    pri_que[i] = data;
```
```
}
```
```
 
```

/* Function to delete an element from queue */

```
void delete_by_priority(int data)
```
```
{
```
```
    int i;
```
```
 
```
```
    if ((front==-1) && (rear==-1))
```
```
    {
```

        printf("\nQueue is empty no elements to delete");

```
        return;
```
```
    }
```
```
 
```
```
    for (i = 0; i <= rear; i++)
```
```
    {
```
```
        if (data == pri_que[i])
```
```
        {
```
```
            for (; i < rear; i++)
```
```
            {
```

                pri_que[i] = pri_que[i + 1];

```
            }
```
```
 
```
```
        pri_que[i] = -99;
```
```
        rear--;
```
```
 
```
```
        if (rear == -1) 
```
```
            front = -1;
```
```
        return;
```
```
        }
```
```
    }
```

    printf("\n%d not found in queue to delete", data);

```
}
```
```
 
```

/* Function to display queue elements */

```
void display_pqueue()
```
```
{
```
```
    if ((front == -1) && (rear == -1))
```
```
    {
```
```
        printf("\nQueue is empty");
```
```
        return;
```
```
    }
```
```
 
```
```
    for (; front <= rear; front++)
```
```
    {
```
```
        printf(" %d ", pri_que[front]);
```
```
    }
```
```
 
```
```
    front = 0;
```
```
}
```

Runtime Test Cases

1 - Insert an element into queue
2 - Delete an element from queue
3 - Display queue elements
4 - Exit
Enter your choice : 1
 
Enter value to be inserted : 20
 
Enter your choice : 1
 
Enter value to be inserted : 45
 
Enter your choice : 1
 
Enter value to be inserted : 89
 
Enter your choice : 3
 89  45  20 
Enter your choice : 1
 
Enter value to be inserted : 56
 
Enter your choice : 3
 89  56  45  20 
Enter your choice : 2
 
Enter value to delete : 45
 
Enter your choice : 3
 89  56  20 
Enter your choice : 4

Sanfoundry Global Education & Learning Series – 1000 C Programs.

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If you wish to look at other example programs on Stacks & Queues, go to C Programming Examples on Stacks & Queues. If you wish to look at programming examples on all topics of C, go to C Programming Examples.

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