Implementation of Circular Queue in c

Implementation of Circular Queue in c

#include<stdio.h>

#include<conio.h>

#include<string.h>

#define size 5

int f=-1,r=-1,a[5];

void enqueue(int);

int dequeue(void);

void main()

{

 clrscr();

 enqueue(10);

 enqueue(20);

 enqueue(30);

 enqueue(40);

 enqueue(50);

dequeue();

dequeue();

 enqueue(60);

 enqueue(70);

getch();

}

void enqueue(int y)

{

            if(f==0 && r==size)

            {

                        printf("\nQueue is full");

            }

            else if(f!=0 && r==size)

            {

                        r=0;

                        a[r]=y;

                        printf("\nValue enqueued is %d at a[%d]",a[r++],r);

            }

            else if(f==-1 && r==-1)          

            {                         

                        f=0;r=0;                   

                        a[r]=y;

                        printf("\nValue enqueued is %d at a[%d]",a[r++],r);

            }

            else if(f==r)

            {

                        printf("\nQueue is full");

            }

            else

            {

                        a[r]=y;

                        printf("\nValue enqueued is %d at a[%d]",a[r++],r);

            }

}

int dequeue()

{

            if(f==r)

            {

                        f=-1;r=-1;

                        printf("\nQueue is underflow");

                        return 0;

            }

            else

            {

                        printf("\nDequeued value is %d at a[%d]",a[f],f);

                        return a[f++];              

            }                                 

}