Implementation of Simple 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()

{

 int i,j,k,l,m,n;

 clrscr();

 enqueue(10);

 enqueue(20);

 enqueue(30);

 enqueue(40);

 enqueue(50);

            i=dequeue();

printf("\nDequeued value is %d",i);

            j=dequeue();

printf("\nDequeued value is %d",j);

            k=dequeue();

printf("\nDequeued value is %d",k);

            enqueue(60);

            l=dequeue();

printf("\nDequeued value is %d",l);

getch();

}

void enqueue(int y)

{

            if(r==size)

            {

                        printf("\nQueue is overflow");

            }

            else if(f==-1 && r==-1)

            {

                        f=0;r=0;

                        a[r]=y;

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

            }

            else

            {

                        a[r]=y;

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

            }

}

int dequeue()

{

            if(f==r)

            {

                        f=-1;r=-1;

                        printf("\nQueue is underflow");

                        return 0;

            }

            else

            {

                        return a[f++];

            }

}