C program for SCAN disk scheduling algorithm

Introduction to SCAN disk scheduling :

                   In the SCAN algorithm, the disk arm starts at one end of the disk and moves toward the other end,servicing requests as it reaches each cylinder,until it gets to the other end of the disk. At the other end, the direction of head movement is reversed, and servicing continues. The head continuously scans back and forth across the disk. The SCAN algorithm is sometimes called the elevator algorithm, since the disk arm behaves just like an elevator in a building, first servicing all the requests going up and then reversing to service requests the other way.

C program for SCAN disk scheduling :

#include<stdio.h>

int main()

{

            int queue[20],n,head,i,j,k,seek=0,max,diff,temp,queue1[20],queue2[20],

                        temp1=0,temp2=0;

            float avg;

            printf("Enter the max range of disk\n");

            scanf("%d",&max);

            printf("Enter the initial head position\n");

            scanf("%d",&head);

            printf("Enter the size of queue request\n");

            scanf("%d",&n);

            printf("Enter the queue of disk positions to be read\n");

            for(i=1;i<=n;i++)

            {

                        scanf("%d",&temp);

                        if(temp>=head)

                        {

                                    queue1[temp1]=temp;

                                    temp1++;

                        }

                        else

                        {

                                    queue2[temp2]=temp;

                                    temp2++;

                        }

            }

            for(i=0;i<temp1-1;i++)

            {

                        for(j=i+1;j<temp1;j++)

                        {

                                    if(queue1[i]>queue1[j])

                                    {

                                                temp=queue1[i];

                                                queue1[i]=queue1[j];

                                                queue1[j]=temp;

                                    }

                        }

            }

            for(i=0;i<temp2-1;i++)

            {

                        for(j=i+1;j<temp2;j++)

                        {

                                    if(queue2[i]<queue2[j])

                                    {

                                                temp=queue2[i];

                                                queue2[i]=queue2[j];

                                                queue2[j]=temp;

                                    }

                        }

            }

            for(i=1,j=0;j<temp1;i++,j++)

            queue[i]=queue1[j];

            queue[i]=max;

            for(i=temp1+2,j=0;j<temp2;i++,j++)

            queue[i]=queue2[j];

            queue[i]=0;

            queue[0]=head;

            for(j=0;j<=n+1;j++)

            {

                        diff=abs(queue[j+1]-queue[j]);

                        seek+=diff;

                        printf("Disk head moves from %d to %d with seek                                                                                       %d\n",queue[j],queue[j+1],diff);

            }

            printf("Total seek time is %d\n",seek);

            avg=seek/(float)n;

            printf("Average seek time is %f\n",avg);

            return 0;

}

 OUTPUT :